\(\frac{\text{dy}}{dx}\) = (5x + 1)\(^4\) = 20(5x + 1)\(^3\) let u = (5x + 1) = \(\frac{du}{dx}\) = 5 y = u\(^4\) then \(\frac{dy}{du}\) = 4u\(^3\) Therefore, \(\frac{dy}{dx} = \frac{dy}{du}\times\frac{du}{dx}\) = 5 x 4u\(^3\) = 20(5x + 1)\(^3\)