I = PRT is the formula for interest, and we need to solve it for R. Since all three of P, R, and T are multiplied, we send things to the other side of the equals through dividing.
I = PRT
I / P = RT to divide both sides by P
I / PT = R to divide both sides by T
So I / PT = R (the first choice) is the equation solved for R.
I=prt
solving for r
we need to isolate r on the left side
so dividing both sides by pt , we get
r=I/pt