Don't you understand how to do it?
1, find the fraction of a number, which can be divided by several (denominator).
For example:
What is a quarter of 12?
Formula: 12÷4=3
A quarter of 12 is 3.
2. Ask for a fraction of a number, which can be divided by the denominator and then multiplied by the numerator.
For example:
How much is five sixths of 48?
Formula: 48÷6×5=40
Five sixths of forty-eight is forty.