Problem
Because the answer must be in inches, first change 5 miles into inches using 1 mile = 63360 inches.
Lengths can only be compared or scaled when they share the same unit, so I switch miles into inches first.
5.MD.A.1Analyze The UnitsThe scale says the map length is one 63360th of the real one, so multiply 316800 by 1/63360.
Multiplying by 1/63360 just divides by 63360, which shrinks the real length down to map size.
5.NF.B.6Identify SubproblemsThe map length is the real length multiplied by 1/63360.
A scale of one over 63360 says that one length on the map stands for 63360 of that same length in the world, so the map length is the real length cut into that many equal parts with one taken.
Both lengths have to be counted in the same unit before the scale can be applied at all, which is why the miles are turned into inches first.
Multiplying by a fraction less than 1 makes the result smaller, so the map length should be far less than the real length in inches.
Resizing by a scale below 1 shrinks the figure, which is exactly what a map does to real distances.
5.NF.B.5Analyze The UnitsMap length = real distance times the scale — just make sure both are in the same unit first.