The Answer is C: 3
Proof:
Solve for x:
7 x - 3 (x - 6) = 30
-3 (x - 6) = 18 - 3 x:
7 x + 18 - 3 x = 30
Grouping like terms, 7 x - 3 x + 18 = (7 x - 3 x) + 18:
(7 x - 3 x) + 18 = 30
7 x - 3 x = 4 x:
4 x + 18 = 30
Subtract 18 from both sides:
4 x + (18 - 18) = 30 - 18
18 - 18 = 0:
4 x = 30 - 18
30 - 18 = 12:
4 x = 12
Divide both sides of 4 x = 12 by 4:
(4 x)/4 = 12/4
4/4 = 1:
x = 12/4
The gcd of 12 and 4 is 4, so 12/4 = (4×3)/(4×1) = 4/4×3 = 3:
Answer: x = 3