I need my system to calculate price, which is dependent on service duration of service item and no o

currently the calculation of price depends on number of quantity of service item, Not on the duration.

what i need is suppose you have 5 quantity of service item and service duration is 12 months and in point break 0-12 months has $2 value then total list price should be 5*2 = $10

and if the service duration is 13 months and in point break 13-24 has value $3 then total list price should be 5*3 = $15.