ampl: reset; model SpoilerInc.mod.txt;data SpoilerInc.dat.txt; 
ampl: expand TotalCost, Starting_Inventory, NoUnitsAtEnd, RegTimeLimit, Balance;
minimize TotalCost:
	50*x[1,'RT'] + 70*x[1,'OT'] + 50*x[2,'RT'] + 70*x[2,'OT'] + 
	50*x[3,'RT'] + 70*x[3,'OT'] + 50*x[4,'RT'] + 70*x[4,'OT'] + 11.04*s[1]
	 + 11.04*s[2] + 11.04*s[3] + 11.04*s[4];

subject to Starting_Inventory:
	s[0] = 12;

subject to NoUnitsAtEnd:
	s[4] = 0;

subject to RegTimeLimit[1,'RT']:
	x[1,'RT'] <= 25;

subject to RegTimeLimit[2,'RT']:
	x[2,'RT'] <= 25;

subject to RegTimeLimit[3,'RT']:
	x[3,'RT'] <= 25;

subject to RegTimeLimit[4,'RT']:
	x[4,'RT'] <= 25;

subject to Balance[1]:
	0.85*x[1,'RT'] + 0.85*x[1,'OT'] + 0.92*s[0] - s[1] = 30;

subject to Balance[2]:
	0.85*x[2,'RT'] + 0.85*x[2,'OT'] + 0.92*s[1] - s[2] = 28;

subject to Balance[3]:
	0.85*x[3,'RT'] + 0.85*x[3,'OT'] + 0.92*s[2] - s[3] = 40;

subject to Balance[4]:
	0.85*x[4,'RT'] + 0.85*x[4,'OT'] + 0.92*s[3] - s[4] = 35;

ampl: solve; display x,s;
Gurobi 10.0.0: optimal solution; objective 8084.133365
6 simplex iterations
x :=
1 OT    0
1 RT   25
2 OT    5.46259
2 RT   25
3 OT   22.0588
3 RT   25
4 OT   16.1765
4 RT   25
;

s [*] :=
0  12
1   2.29
2   0
3   0
4   0
;


# Interpretation: The minimum total cost for Spoiler Inc. is $8084.13,
# with the production schedule as shown above. Note that the total
# cost to produce in regular time and store is 50 + 12, which is
# smaller than the unit cost of production in over time. Hence the
# regular time production is maxed out at the limit of 25 units in
# each quarter.