To make the y terms cancel out, multiply
the first equation through by -3 and the
second equation through by +4:
Add those two equations vertically term by term and get:
To make the x terms cancel out, multiply
the first equation through by -4 and the
second equation through by +5:
Add those two equations vertically term by term and get:
The solution is (x,y) = (-7,9)
Checking:
The solutions check