Question

In 3 seconds, a wave generator produces 15 pulses that spread over a distance of 45 centimeters. Calculate its velocity.

Answer 1

We don't even need to know how many pulses were produced
in those 3 seconds.

The beginning of the first pulse took 3 seconds to travel
45 centimeters from the generator.

Its speed is    (45 cm) / (3 sec)  =  15 cm/sec.