start by factoring -24
6* -4 = -24
7*-3 = -24
you are looking for factors that add to give the middle coefficient +5
7 and -3 add to give 5 and multiply to give -24
( x + 7)(x - 3) = 0
this gives the solution for x, because one or both (x + 7) and/or (x - 3) would have to be zero for them to multiply and be zero.
x = -7
x = 3