when I am Using Service Contract With Extended Amount And Create Work Order For This Contract how to

when I am Using Service Contract With Extended Amount And Create Work Order For This Contract how to cut the work order price from contract amount ?

Example :

Contract For Customer X with Price Amount 10000 for one Month and This Customer create service order with Price 8000 how to make this work order cut this amount (8000) from Contract Price (10000)

and when this customer come again to create new work order with 5000 amount then create the invoice with 3000 only,

Contract With amount 10000 at One Month

First work order price 8000

i want JDE To do That :

contract available amount is 2000

second work order amount is 5000