please answer 3.b:

3. (3.a) For a MA(3) process with coefficients 01 = 2, 02 = 0.5, and 03 = -0.1, (i) write the mathematical equation for MA(3) model with these coefficients, and (ii) calculate the autocorrelation function at lags 1, 2, 3, 4: p(1), p(2), p(3) and p(4). (3.b) For an AR(1) process with coefficient $1 = -0.5, (i) write the mathematical equation for AR(1)) model with these coefficients, and (ii) calculate the autocorrelation function at lags 1, 2, 3, 4: p(1), p(2), p(3) and p(4)