Simplifying
x + 2x = 5 + 10

Combine like terms: x + 2x = 3x
3x = 5 + 10

Combine like terms: 5 + 10 = 15
3x = 15

Solving
3x = 15

Solving for variable 'x'.

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

Divide each side by '3'.
x = 5

Simplifying
x = 5