Define the decision variables and objective function for this problem

Andy Tyre manages Tyre's Wheels, Inc. Andy has received an order for 1000 standard wheels and 1200 deluxe wheels for next month, and for 750 standard wheels and 1000 deluxe wheels the following months. He must fill all the orders. The cost of regular time production for standard wheels is $25 and for deluxe wheels, $40. Overtime production costs 50% more. For each of the next two months there are 1000 hours of regular time production and 500 hours of overtime production available. A standard wheel requires .5 hour of production time and a deluxe wheel, .6 hour. The cost of carrying a wheel from one month to the next is $2.

Answer: Define the decision variables:
S1R = number of standard wheels produced in month 1 on regular time production
S1O = number of standard wheels produced in month 1 on overtime production
S2R = number of standard wheels produced in month 2 on regular time production
S2O = number of standard wheels produced in month 2 on overtime production
D1R = number of deluxe wheels produced in month 1 on regular time production
D1O = number of deluxe wheels produced in month 1 on overtime production
D2R = number of deluxe wheels produced in month 2 on regular time production
D2O = number of deluxe wheels produced in month 2 on overtime production
Y1 = number of standard wheels stored from month 1 to month 2.
Y2 = number of deluxe wheels stored from month 1 to month 2.
MIN 25 S1R + 37.5 S1O + 40 D1R + 60 D1O + 25 S2R + 37.5 S2O + 40 D2R + 60 D2O + 2 Y1 + 2 Y2