\(\frac{\text{dy}}{dx}\) =  (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)\(^3\)