Find y.

5x-3y=21

(explanation would be too.)

Here is a possible

x=9 (5x = 45)
y=8 (3y=24)

Subtract 24 from 45 and you get 21; this is how you check to make sure your answer is correct–by finding x

so, y = 24
 I just used the guess and check strategy to get my answer

please mark as brainliest or give good rating if this helped you. I hope it did!