Simplifying
10x + 3x = 100 + 69

Combine like terms: 10x + 3x = 13x
13x = 100 + 69

Combine like terms: 100 + 69 = 169
13x = 169

Solving
13x = 169

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Divide each side by '13'.
x = 13

Simplifying
x = 13