Hello, I can't figure out how to solve this homework problem.

4. For the op-arnp circuit shown in Fig 4: a. Find the differential equation for the circuit output, V0 (t), in terms of R1, R2 and R3 if Vs = u(t). b. Find the solution for the zero-state response, V0 (t). c. What is the expression for the time constant of the circuit? d. If the resistances are constrained to values between 0 and 1 k9, which resistance (R1, R2 or R3) is the time constant most sensitive to, such that it changes the most as this resistance changes. Show your reasoning. e. Let R1 = R2 = R3 = R and sketch the response of Vo(t)