Given the model below: Period 1 2 3 4 5 6 7 8 9 10 11 Demand 140 170 190 200 200 160 190 170 190 230 240 Oil price 97 92 81 61 79 84 85 76 61 64 48. a. Compute the forecast for period 12 using a causal regression model and assuming that the oil price for period 12 is 83. (Round regression coefficients and forecasts of demand to two decimal places.) b. Create a graph of the gasoline sales and oil price data and include a line representing the regression model. In which period is gasoline sales least well predicted by oil price? What is the amount of this largest error? (Use your rounded regression coefficients and errors from Part a. Round your largest error answer to 2 decimals. Include the negative sign if that largest error is negative.)