This is a linear equation in x.
x + 6 = 2x-7
Adding -2x to both sides we obtain,
x +6 - 2x = -7
Now let's again add -6 to both sides of the equation, This implies that:
x-2x = -7-6
Let us simplify further to obtain,
-x = - 13
Let's multiply through by -1 to obtain
x = 13
CHECK
13 +6 = 2(13) - 7
13 + 6 = 26 -7
19 = 17