The rate of change of a function given in the form of a linear equation \( y = mx + b \) is represented by the slope \( m \).
In the equation \( y = -\frac{3}{5}x + 10 \), the slope \( m \) is \( -\frac{3}{5} \). Therefore, the rate of change of the function is \( -\frac{3}{5} \). This means that for each unit increase in \( x \), the value of \( y \) decreases by \(\frac{3}{5}\).