The answer is 30. The (14) comes from the amount the Tshirts cost, the 12 is the amount of T-shirts that are printed each hour and 30 is the starting amount of T-Shirts
You can first take out an x^2 from each number , 3x^6 - 39x^4 + 108x^2 = x^2 ( 3x^4 - 39x^2 + 108) Then just factor and solve for the zero's of the equation
