Write MATLAB codes to do the following tasks a) solve the following simultaneous equations: 4x1 + x2 = x3 + 3 x1 - 3x2 - 2x3 + 4=0 x1 - 2x2 - x3 = -6 b) Find the roots of the following polynomial then plot the polynomial, over the range (-10 < x < 40) 4x2 - 3x3 + 15 = 2x2 - 20 c) Write a program that accepts a numerical value x from 0 to 100 as input and computes and displays the corresponding letter grade given by the following table. A x >= 90 B 80 <= x <= 89 C 70 <= x <= 79 D 60 <= x <= 69 F x < 60 D) Use a for loop to determine the sum of the first 12 terms in the series 4(k3 +2), k = 1, 2, 3, . . . , 12.