-3x + 20 = 2
Subtract 20 to both sides to isolate the x
-3x = 18
And then divide by -3 to both sides since -3 is multiplied to x
x = -6
To check you work plug back into the equation
-3(-6) + 20 = 2
-18 + 20 = 2
2 = 2
Which means that it is the right answer