How do I use the chain rule for differentiation?

Let’s say we’re given the equation y=(2x-6)^4we would know how to differentiate x^4, therefore we can take the substitution u=2x-6 to give us the equation y=u^4we then differentiate this equation (dy/du) to get 4u^3
However, we need dy/dx , and so we take the fact that dy/dx = (dy/du) x (du/dx)u=2x-6, therefore du/dx = 2And so dy/dx = 2 x 4u^3 = 8u^3