Answer:
Thus, the payback time for cavity wall insulation is 7.5 years
You need to know how much friction that object.
Pretty sure that it is 0.
Explanation:
A wavefront is the long edge that moves, for example, the crest or the trough. Each point on the wavefront emits a semicircular wave that moves at the propagation speed v. These are drawn at a time t later, so that they have moved a distance s = vt.
