1) step 1 the way you calculate this is by dividing the number in question by the number which comes after the "of"
So:
x percent of y is:

a percent of b is:

and for us:
x percent of y is:

we can also simplify it:

for this i divided both numbers by 15.
2) for the second step you multiply the fraction by 100%, ,which is 1: you can always multiply by 1!

=20%
because 100/5=20
was is clear? let me know if you have more questions!