Evaluate sin 3 pie over 4

Barbara's piano instructors house is 7 1/8 miles from her house. after biking for 1 3/4 miles she stops to rest how much longer does she need to bike to reach her instructor's house

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?

What effect would doubling all the dimensions of a triangular pyramid have on the volume of the pyramid? explain your reasoning.