Final answer:
The speed of the waves is 1.5 mm/s.
Step-by-step explanation:
To find the speed of the waves, we can use the formula:
Speed = Distance / Time
In this case, the distance between two crests is given as 4.5 mm and the time it takes for one crest to pass is given as 3.0 s.
Plugging these values into the formula, we get:
Speed = 4.5 mm / 3.0 s = 1.5 mm/s
Since it is requested to express the answer to two significant figures, the speed of the waves is 1.5 mm/s.