ok so you know this is a factoring problem so you need two parenthesis to multiply together (foil) to equal 12x^2+ax=20 and change that to 12x^2+ax-20 to be able to find the factors of this exuation. so set it up to be (3x+4)(_x-_) the blanks are going to be numbers that u fill in. so u need a number that multilies by the first term, 3, and the only option is for the first blank to be 4 in order for you to get 12 as the squared term. now u need a number that multiplies to get a -20 (bc u moved it over to the left side of the equation). so the only option u have for that number is a -5 (to get a -20 u need a negative number for the second blank) so u r left with (3x+4)(4x-5)=0. there is ur equation and when u foil it u get 12x^2-15x+16x-20=0 and then combine -15x and 16x to get a +1x or just x. so that a is equal to 1. i tried to explain this as best as i could in words. hope this helps!!
