Answer
$v_p=4\frac{cm}{s}$
Work Step by Step
The speed to be found, $v_p$, is the probable speed.
The data in the question makes it clear that there are more particles at speed $4\frac{cm}{s}$ than at any other speed ( there are at $8$ particles at this speed).
Therefore, the most probable speed is $v_p=4\frac{cm}{s}$
