How do you solve 40x plus 30y equals 1600?

Answer 1

You can't. All you can tell is the relationship between 'x' and 'y'.

x = 40 - 0.75y

y = 1/3 of (160 - 4x)

There are an infinite number of pairs of numbers that 'x' and 'y' can be.

In order to find out a single pair of numbers that 'x' and 'y' must be, you need another equation.

You need the same number of equations as the number of 'unknowns' you're trying to find.