To solve this, you need to isolate/get the variable "x" by itself in the equation:
-3(x + 5) = -9 Distribute/multiply -3 into (x + 5)
(-3)x + (-3)5 = -9
-3x - 15 = -9 Add 15 on both sides
-3x - 15 + 15 = -9 + 15
-3x = 6 Divide -3 on both sides to get "x" by itself

x = -2
I just realized I took unnecessary steps....you could've just divided -3 then subtracted 5
-3(x + 5) = -9 Divide -3 on both sides [two negative signs cancel each other out and become positive]
x + 5 = 3 Subtract 5
x = -2