Answer
$$312.5\ rpm
.$$
Work Step by Step
The relationship of two rotating pulleys connected by a belt is:
(diameter of A)(rpm of A) = (diameter of B)(rpm of B).
Now we have
$$
25\times 600=48\times x\Longrightarrow x=\frac{25\times 600}{48}=312.5 \ rpm
.$$
