Break it down
"15 less than " means -15
"a number" means unknown or placeholder means x
"is equal to" means '='
'12' means 12
-15+x=12
add 15
x=27
It could be twenty two times forty feet is equal to 2500 cubic feet since it is volume
So the ratio of boys to girls is 12:24.. now, is that an equivalent ratio as 2 boys for 4 girls? or 2:4? let's see.

you could start simplifying the 12/24 fraction by dividing by some common multiple, say 2, and get 6/12, then divide by 3 and get 2/4 and stop there.
then you'll notice that 12/24 is really 2/4 in disguise.
F(x) - g(x) = -2x^3 - 6x^2 + 9x