Since you already know the solution, you need to substitute every occurrence of x and y with those values: the first equation checks out, because it becomes
[tex] 3\cdot 4 - 2 \cdot 2 = 12-4 = 8 [/tex]
The second becomes
[tex] 2 \cdot 4 + 3 \cdot 2 = Q \iff 8+6 = Q \iff Q = 14 [/tex]
