I come across this type of question pretty often, and while my way of solving is correct and gives me the right answer, it’s a bit tedious and I was wondering if there is a easier method
My method:
if x=3 is one solution, then the equation must be divisible by (x-3)
The I basically do long division of x^2 + rx -24 by x -3
The remainder I get is 3r - 15
As x-3 perfectly divides the equation 3r - 15 =0
x = 5