Product rule is dy/dx = uv' + vu'
So y = x(7-4x)9
u = x, v = (7-4x)9 u' = differentiation of u, v' = differentiation of v
dy/dx = x.9(7-4x)8.-4 + (7-4x)9.1 <--- used the product rule, don't forget to use function of a function rule when differentiating (7-4x)9
= -36x(7-4x)8 +...