Answer
$f_{s,max}$ increases as more force is applied to the crate.
Work Step by Step
The equation to guide the thinking in this problem is:
$f_{s,max}$=Coefficent of Friction$\times$Normal Force
The coefficient of friction remains constant throughout the experiment, and the normal force has a direct relationship with $f_{s,max}$. This means that as normal force increases, $f_{s,max}$ increases. When more force is applied on the crate normal force increases, meaning that increasing force on the crate increases $f_{s,max}$.
