CALCULUSSuppose you make monthly deposits of P dollars into an account that earns interest at a monthly rate of p%. The balance in the account after t years is B(P, r, y)=$P \left( \frac { ( 1 + r ) ^ { 12 t } - 1 } { r } \right)$, where r=p/100 (for example, if the annual interest rate is 9%, then $p = \frac { 9 } { 12 } = 0.75$ and r=0.0075). Let the time of investment be fixed at t=20 years. a. With a target balance of $20,000, find the set of all points (P, r) that satisfy B=20,000. This curve gives all deposits P and monthly interest rates r that result in a balance of$20,000 after 20 years. b. Repeat part (a) with B=$5000,$10,000, $15,000, and$25,000, and draw the resulting level curves of the balance function.