Solve -5x-9y=-21 and 7x+5y= -1
-5x-9y=-21 -- times 7 ---> -35x - 63y = -147
7x + 5y = -1 -- times 5 ---> 35x + 25y = -5
add them:
-38x = -152
x = 4
sub into the original 2nd to get y
7x + 5y = -1 -- times 5 ---> 35x + 25y = -5
add them:
-38x = -152
x = 4
sub into the original 2nd to get y