I don't know how to substitute and eliminate
2x-3y=5
4x-6y=21
Can some one show me how to solve for x and y

Kristen

2x-3y=5
4x-6y=21

Nobody can help you with that, as the data you provide is incorrect.
If 2x-3y=5 , than the double of (2x-3y) = 2(2x-3y) = 4x-6y should be 2x5 = 10.
But your data states 21.
Is there a sign incorrect ?