ok im having the hardest time getting an answer for this problem

A marketing firm estimates thatnmonthsafter the introduction of a clients new product, f(n)thousand household will use it, where

f(n) = 10/9n(12 - n), 0<=n<=12

<=, less than equal, or greater than equal

10/9 is a fraction.

b. How long will it take for household use to reach a maximum?

c. How many households will use the product when it reaches its maximum?

d. The client must have 3 thousand households using the product in order to break even. How many months will it take before 3 thousand households use the product? (Give the decimal value of n.)

i got answers for b and c, but i can't get d... ive tried the quadratic formula and im stumped

a.) was graph the equation which i got already

Thanks for anyhelp