Find the derivative of the given function: y = 4 * 6ˣ - 9x³.

a) (dy/dx) = 4 * 6ˣ * ln(6) - 27x²
b) (dy/dx) = 4 * 6ˣ * ln(6) - 9x²
c) (dy/dx) = 4 * 6ˣ * ln(6) - 27x³
d) (dy/dx) = 4 * 6ˣ * ln(6) - 9x³