Answer:
D. 6
Explanation:
The system can be solved by subtracting double the second equation from the first:
... (4x +3y) -2(2x +y) = (20) -2(7)
... y = 6 . . . . . . . . . for solution (x, y) = (a, b), this tells you b=6.
Putting this into the second equation gives ...
... 2x +6 = 7
... 2x = 1
... x = 1/2
The solution is (x, y) = (a, b) = (1/2, 6). b = 6.