Find the ratio a: b- 1) 2a=9b 2) a+b=3b explain your work

Adan has decided to purchase an $9000 car. he plans on putting 20% down toward the purchase and financing the rest at 7.9% interest rate for 3 years. find his monthly payment a) $225.29 b) $298.81 c) $204.78 d) $236.89