(1 point) Your monthly car payment in dollars is P = f(Po, t,r), where $Po is the amount you borrowed, t is the number of months it takes to pay off the loan, and r percent is the interest rate. (a) is dPldt positive or negative? ? Suppose that your bank tells you that the magnitude of Plt is 50. What are the units of this value? (For this problem, write our your units in full, writing dollars for $, months for months, percent for %, etc. Note that fractional units generally have a plural numerator and singular denominator.) (b) is Plr positive or negative? ? Suppose that your bank tells you that the magnitude of Plr is 15. What are the units of this value? (For this problem, write our your units in full, writing dollars for $, months for months, percent for %, etc. Note that fractional units generally have a plural numerator and singular denominator.) For both parts of this problem, be sure you can explain what the practical meanings of the partial derivatives are