A manager is applying the transportation model of linear programming to solve an aggregate planning problem. Demand in period 1 is 100 units, and in period 2, demand is 150 units. The manager has 125 hours of regular employment available for $10/hour each period. In addition, 50 hours of overtime are available for $15/hour each period. If holding costs are $2 per unit each period, how many hours of regular employment should be used in period 1? (Assume demand must be met in both periods 1 and 2 for the lowest possible cost and that production is 1 unit per hour.)