Question 49594
1st: x-y=4
2nd: x-2y=10 

Solve the 1st for x to get; x=y+4
Substitute that value of "x" into 2nd, as follows:

(y+4)-2y=10
-y+4=10
y=-6

Subtitute that value of "y" into 1st to get:
x+6=4
x=-2
Then the solution for the system of equations
is x=-2, y=-6
Check the answer in 2nd as follows:
-2-2(-6)=10
-2+12=10
10=10

cheers,
Stan H.