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!!
You just put the numbers in order from least to greatest and its the middle one. if there's an even amount of numbers, you add the middle two and divide by 2
