Graph each of the following systems of equations for all values of x indicated.
a. y - 4x = 0 and y - 2x - 10 000 = 0 for x = 0 to x = 10 000
b. 4x + 2y = 200 for x = 0 to x = 50 and x + 2y = 80 for x = 0 to x = 80
c. 3x + 3y = 2400 and x = 500 for x = 0 to x = 800
d. 2y = 5x and y = 5000 for x = 0 to x = 8000