Question

2y = 6
3(x+y) = 12

A. One solution
B. Infinity solutions
C. No solutions

Answer 1

Solve and see. First equation, 2y = 6, obvious to the most casual observer y must be 3.
Substitute 3 for y in the lower equation 3(x + 3) = 12
remove the parentheses 3x + 9 = 12. Now subtracting 9 from both sides of the = sign:
3x = 3 divide both sides by 3 gives x = 1
Looks like one solution to me (1, 3), do you see any other solution to the system??