3/5 because it can't be 1/6 or 1/2 because they are 50% or smaller. Also it is 2/5 because if you count 20, 40, 60... up to 100 the third number is 50.
I guess you would isolate the variable. So switch the equation around to f=L/24
(3^3 - 9 )^2
First do what is inside the parenthesis:
3^3 = 27
Now you have:
(27-9)^2
Subtract:
27-9 = 18
Now you have:
(18)^2
Raise 18 to the second power:
18^2 = 324