Someone please answer these two questions for me

The sales tax for an item was $8.40 and it cost $420 before tax. find the sales tax rate. write your answer as a percentage.

Aregular octagon rotates 360 degrees about its center. how many times does the image of the octagon coincide with the preimage during the rotation?

We can calculate the depth dd of snow, in centimeters, that accumulates in harper's yard during the first hh hours of a snowstorm using the equation d=5hd=5h. how many centimeters of snow accumulate per hour?