Question

I have no idea on how to solve this A=P+Prt solve for r

Answer 1

Start with your railroad tracks, and subtract P from both sides giving you A-P=Ptr, and now now divide both sides by Pt, which will give you r=A-P/Pt

Answer 2

A=P+Prt ----> A-P=Prt ----> (A-P)/(Pt) =r