How to determine a map scale

I'm making a topographic map for school. The paper is 3ft by 3ft. The area's dimensions are 30ft by 121 ft. What should the scale be? 1 in=5 ft?

1 in = 4 ft

Then 120 ft. would use 30" of the 36" paper.

30 ft. x 121 ft. would be 7.5" x 30.25"