Answer
$576\ teeth$
Work Step by Step
The relationship of a gear system is:
(no. of teeth in A)(rpm of A) =(no. of teeth in B)(rpm of B).
Now, we have
$$
x\times 6.25=120\times 30\Longrightarrow x=\frac{120\times 30 }{6.25}=576\ teeth
.$$