7x + 2(-2x + 1) = 29
7x - 4x + 2 = 29
7x - 4x = 29 - 2
3x = 27
3x/3 = 27/3
x = 9
The equation has got one solution.
We know that ax = b, in this case 3x = 27
To find x you would follow the rule x = b/a
If a is ≠ 0, then the eqaution is determinated and has one solution!