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

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.