Compute and plot the impulse responses of R_rf, DP, and R_t in response to a shock to R_rf for 20 periods ahead. Hint: to compute the impulse responses, evaluate C_0 = A^(-1), C_1=A^(-1), C_2=^2 A^(-1), ..., C_20=^20 A^(-1). To isolate just the effect of a shock to R_rf, only save the first column of each matrix C_i. It will have three elements, corresponding to your three variables R_rf, DP, and R_t