Find dy/dx.
y = (x³) (1/4) (7 - 9x)
a) (1/4) (7 - 9x) (x²) (-3/4)
b) (1/4) (7 - 9x) (x²) (-1/4)
c) (1/4) (7 - 9x) (x²) (1/4)
d) (1/4) (7 - 9x) (x²) (3/4)