How do you solve by substitution #4x-9y=-21# and #4x+3y=-9#?
We firstly obtain x or y from (A):
And then we put this result at the place of x in (B).
It is not the end! Now that we found y we have to find x. We can basically substitute y=-5/2 in one of the two equations (for example
So the solution of the system is