PLS HELP EASY ALGEBRA LOTS OF POINTSSS AND BRAINLIEST

Answer:
Boy that's CAAAPPPPP.
Step-by-step explanation:
Answer:
The answer is a = 12 and b = 9.
Step-by-step explanation:
For starters 12 + 9 equals 21 and when you multiply 3/4 by 12 it gets you nine so both those statements are accurate if you choose this answer.