Answer
If the width $w$ of the terraces were smaller, the frequency would be higher.
Work Step by Step
The path length difference between each pulse is $\Delta L = 2w = 1.5~m$
We can find an expression for the number of pulses per second:
$f = \frac{v}{\Delta L}$
$f = \frac{v}{2w}$
We can see that as the value of $w$ decreases, then the value of the frequency $f$ increases.
Therefore, if the width $w$ of the terraces were smaller, the frequency would be higher.
