We are given the equation,
(3x + 15) + (4x - 9) = 90; Find x
Firstly, we need to open the parentheses
3x + 15 + 4x - 9 = 90
Secondly, we need to collect the like terms
3x + 4x + 15 - 9 = 90
7x + 6 = 90
Make 7x the subject of the formula
7x = 90 - 6
7x = 84
Divide both sides by 7
7x/7 = 84/7
x = 84/7
x = 12
The answer is 12