3. SOLVING STOCHASTIC DIFFERENTIAL EQUATIONS (20 POINTS) In this exercise you will solve a stochastic differential equation. Assume you model interest rates with the following mean-reverting stochastic differential equation drt (a Brt)dt + σdWt. = (1) Use the Ito formula to derive d(ert). Simplify your formula so that it does not involve rt. (2) Integrate the equation you obtain in (1) and solve for rt.