The units that are Obtained by combining other units is called Derived Units.
incompatible units one is measure of time the other of length.
You can't convert that. You can only convert units that measure the same type of thing - for example, units of length to units of length, units of mass to units of mass, units of time to units of time, etc.
It doesn't make sense to convert that. You can only convert units of the same kind, e.g., units of length to units of length; units of area to units of area; units of time to units of time, etc.
Density
That depends on what you are talking about. If you are talking about units of time, then it could be hours, though it could be other units of time. You could also be talking about units of some other kind entirely, that have nothing to do with time.
Mass, length, and time are considered fundamental units because they are independent and cannot be derived from other physical quantities. These three fundamental units serve as the building blocks for the International System of Units (SI) and form the basis for measuring other physical quantities.
The principal SI units used to derive all other SI units are the base SI units. These are the units for physical quantities such as length, time, mass, electric current, temperature, amount of substance, and luminous intensity.
If this is a speed problem, use the formula: distance = speed x time. Other than that, you can't convert from units of distance to units of time.
The units that are Obtained by combining other units is called Derived Units.
In the SI, it is DEFINED as a base unit, together with the unit of length, the unit of time, and a few others. Other units are derived from these base units.
It, as with many other units of measure, is a standard to which everyone can agree.
Time is typically measured in seconds in the metric system. Other units that can be used for longer time intervals include minutes, hours, or days, but they are not part of the official SI units for time.
Fundamental units are the basic units of measurement in a system of units, typically defined independently of other units. In the International System of Units (SI), the fundamental units include the meter for length, kilogram for mass, second for time, ampere for electric current, kelvin for temperature, mole for amount of substance, and candela for luminous intensity. These units form the basis for deriving all other units of measurement.
The SI unit of time is the second. Other units of time that are often used are minute, hour, day, week, month, year, century, millenium, as well as decimal fractions of a second such as the millisecond, microsecond, or nanosecond.
incompatible units one is measure of time the other of length.
In SI, acceleration is measured in meters / second2, or meters / second / second. In other units, units of the same dimension have to be used, i.e., [length] / [time] / [time]. For example, in the imperial units, feet per square second is quite common.