2023年6月A卷 · 第 21 题

The expression \( \frac{x^{20}\left(x-4\right)}{5x^2}+\frac{4x^{20}}{5x^2} \)   is equivalent to \( \frac{1}{5}x^c \) , where \( c \) is a constant and \( x \) ＞0. What is the value of \( c \) ?