please help 28 - 32 thanks

historical data accumulated over a period of time, (28) (7) forecasting methods use equations that consist of one or more explanatory variables that can be used to predict demand. (29) (7) is the ratio of actual output to design capacity. (30) (7) is the ratio of actual output to effective capacity, (31) (?) is an amount of capacity in excess of expected demand when there is some uncertainty about demand. (32) The volume at which total cost and total revenue are equal is referred to as the (?)