How to solve the equation x / 3 = 2 (x + 15) / 7

How to solve the equation x / 3 = 2 (x + 15) / 7

Cross phase multiplication makes 3 * 2 (x + 15) = 7 * X
6X+90=7X
X=90

The solution of the equation 7 / x + 12 / (x + 15) = 2
The distance between a and B is 19 kilometers. From a to B, you can walk 7 kilometers first and then ride a bicycle for 2 hours. You know that the speed of cycling is 15 kilometers faster than that of walking per hour
We need to solve the equation

x=5

How to solve the equation (x-7-5-4) 6 + 2 × 4 + 1 × 15 = (x-3-4-1) × 3 + 3 × 8 + 4 × 9 + 10?

First, we merge and simplify
(X-16)6+23=(X-8)3+70
Merger of transferred items
6X-3X=70-24+16×6-23
3X=119
X=119/3