The formula I=PrtI = PrtI=Prt gives simple interest. Solve for rrr.
r=fracIPtr = \\frac{I}{Pt}r=fracIPt
r=IPtr = IPtr=IPt
r=fracPtIr = \\frac{Pt}{I}r=fracPtI
r=I−Ptr = I - Ptr=I−Pt