Before we begin, note that:
-ve * +ve = -ve
+ve * -ve = -ve
+ve * +ve = +ve
-ve * -ve = -ve
Now, the given is:
90 = 5x - (2x-30)
To solve for x, we will need to separate the x on one side of the equation and get its value as follows:
90 = 5x - (2x-30)
90 = 5x - 2x + 30
5x - 2x = 90 - 30
3x = 60
x = 60/3
x = 20
