The product of one more than a number and 4 less than the number is 36. Find the number
Let the number be x
(x+1)(x-4) = 36
x^2 - 3x - 4 = 36
x^2 - 3x - 40 = 0
(x-8)(x+5) = 0
x = 8 or x = -5
check: if the number is 8
then is 9 times 4 = 36 ? yes
If the number id -5,
is -4 times -9 = 36 ?, yes
the number could be 8
or it could be -5
Solve
(N+1)(N-4)=36
Expand and simplify
N^2-3N-40=0
(N-8)(N+5)=0
Solve N-8=0 or N+5=0 to give N=8 or N=-5.