Need to know how to find the soution

A computer help-service charges an initial fee to join the service plus an additional charge for each hour of helpservice a customer uses. If the computer service company charges a total of $140 for the initial fee and a 2-hour help session and a total of $220 for the initial fee and a 4-hour help session, which of the following expressions gives the computer company's charge for each hour of help-service that a customer uses?

A. $220-$140/ 4-2

B. $220+ $140 /4+2

C. 4-2/ $220 -$140

D. 4+2/ $220+ $140