Starting equation: 

(3)(5) 
x 3 
 (3)(5) 
x  5 5 
= (3)(5)(3) 
Remove parentheses using "a(b+c)=ab+ac":
5x  3x 3(5) = 45
5x  3x + 15 = 45
2x + 15 = 45
Subtract 15 from both sides:
2x + 15  15 = 45  15
2x = 30
Finally, divide both sides by 2:
x = 15 