Expand the script such as the constants "a, " "b, " and "c" are defined by the user. Test your script for the values defined in the problem. Using MATLAB for Financial Advising The monthly payment, M, of a loan amount (or principal), "P, " for "n" years at a fixed annual rate of interest "r" can be calculated by the formula M = P (r/12) (1 + r/12)^12n/(1 + r/12)^12n - 1 (a) Calculate the monthly payment of a $20,000 (four years of college) loan (P) for 15 years at an interest rate of 6.8% (r = 0.068, the interest of an unsubsidized Stafford loan). (b) Calculate the total amount needed for re-paying loan (total payments through 15 years)