615 is a whole number and as such has no need to be converted to a decimal. It could be represented as 615. but it ends in a five and so the terminal decimal is meaningless.
0.344 is a decimal.
163.7 is a decimal.
It is already in decimal form.
To convert a decimal to a percent, multiply the decimal by 100. The result is the conversion as a percent. In this case the result is 615%
Written as a decimal 7/10 would be .70
In a decimal form, that quantity would be written as-0.12
The fraction would be written as 4/400 and would be 0.01 as a decimal.
0.018 is already written as a decimal. As a fraction, it would be 18/1000 or 9/500.
It would be 0.0012