PLEASE HELP!!!
SOMEONE!!!

Answer:
7,0
Step-by-step explanation:
Let's solve for a.
3a−4b=21
Step 1: Add 4b to both sides.
Step 2: Divide both sides by 3
Let's solve for b.
3a−4b=21
Step 1: Add -3a to both sides.
Step 2: Divide both sides by -4.