The correct option is A −72
First, convert the words into an equation:
n3=n2+12
From here, you could work with the answers by substituting them into the equation, until it works or use algebra to solve the equation:
n3−n2=2n6−3n6=−n6=12
So that n=−72. (You could also solve the equation by multiplying through by 6 first to get rid of the fractions.)