Using the interest formula $A=P(1+r t)$, solve for the indicated variable. Solve for $\mathrm{r}$. \[ r= \] (Simplify your answer.)

Step 1 ：The question is asking to solve for r in the interest formula. To do this, we need to isolate r on one side of the equation. We can do this by subtracting P from both sides, then dividing by Pt.

Step 2 ：The solution is \( r = \frac{A - P}{Pt} \)

Step 3 ：Final Answer: \(\boxed{r = \frac{A - P}{Pt}}\)