You can put this solution on YOUR website! You can approach this by trial and error. First, consider what the factors of 15 are: either 3*5 or 1*15. The factors of 16 are either 4*4 or 2*8 or 1*16. So, you will have factoring like:
(3x +/- 2)(5x +/- 8)
(3x +/- 4)(5x +/- 4)
etc.
Note that the -16 tells us that one of the factors has a + and the other has a -. Also, we know that the +x's will out number the -x's by 8 (i.e., the middle term is +8x.
By trial and error:
(3x + 4)(5x - 4) = 15x^2 - 12x + 20x - 16 = 15x^2 + 8x - 16.
Well, what luck! Found it on the first try!
The factors are (3x+4)(5x-4).
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