I understand how to do it's just I don't understand what a certain part of my homewor kmeans.

What does f(u) mean? I plug in u for the values of x?Using the method of u-substitution,

$\displaystyle \(\displaystyle \int_{2}^{4} (5 x - 7)^{4} \, dx = \int_{a}^{b} f(u) \, du\) $

where

$\displaystyle u = 5x-7$ (enter a function of x)

$\displaystyle du = 5$ dx (enter a function of x)

$\displaystyle a =2$ (enter a number)

$\displaystyle b =4$ (enter a number)

$\displaystyle f(u) =?$ (enter a function of u).

The value of the original integral is .