How can you determine a unit rate for a situation

Which is an equation for the nth terms of the sequence 12,15,18,21

Awindow washer cleans 42 windows in 2 hours. at this rate, how many windows did he clean in 180 minutes.

The construction of copying qpr is started below. the next step is to set the width of the compass to the length of ab. how does this step ensure that a new angle will be congruent to the original angle? by using compass take the measures of angle and draw the same arc according to it.