It looks like the differential equation is
Factorize the right side by grouping.
Now we can separate variables as
Integrate both sides.
You could go on to solve for 
explicitly as a function of 
, but that involves a special function called the "product logarithm" or "Lambert W" function, which is probably beyond your scope.
Answer:
108
Step-by-step explanation:
a = b*h
a = 9*12
a= 108m^2
