The given trinomial is quadratic. Factorization will be as follows:
Multiplying the co-efficient of x^2 and the constant results in 180. We have to make factors of 180 in such a way that their sum of difference is equal to the co-efficient of x.
You can do a proportion: 75/15 = x/100 you then do 100x75 and the divide by 15 and get 500. 15% of $500 is $75 so the sale price would be $425 I believe.