Explanation:
4 + x + 3x = 4 ( 5x ) - 3 ( x ) - 10
4 + x + 3x = 4 + 5x - 3 + x - 10
x + 3x + 5x + x = 4 + 4 - 3 - 10
10x = 21
10x % 10 = 21 % 10
x = 2,1
3.5m questions
4.4m answers