Isaiah is trying to decide if the interval use plan is better than the standard use plan for his electricity consumption. calculate the monthly costs of both plans if he uses 1,275 kwh of electricity per month with 575 kwh on-peak usage and the rest off-peak usage. standard use plan interval use plan 7. 5 cents/kwh for the first 400 kwh 10 cents/kwh for anything over 400 kwh on-peak hours - 15 cents/kwh off-peak hours - 3 cents/kwh a. standard use plan - $117. 50; interval use plan - $107. 25 b. standard use plan - $87. 50; interval use plan - $86. 25 c. standard use plan - $117. 50; interval use plan - $86. 25 d. standard use plan - $87. 50; interval use plan - $107. 25.