3x + 5y = 78
2x - y = 0
the point of intersection of the lines has an x-coordinate of
78
6
-6

Hello here is a solution :
3x + 5y = 78 (1)
2x - y = 0 ... (2)
from (2) : y = 2x
in (1) : 3x+5(2x) =78
            13x = 78
x= 6
 but : y =2x    y=2(6) = 12
answer : x=6

Iagree that is the answer to the question