easy question about math, please help?!?

[hunny =)]

i have the question that says:
A store received $823 from the sale of 5 tape decks and 7 radios. The receipts from the tape decks exceeded the receipts from the radios by $137. What is the cost of a radio?
ok, i tried to mke it into 2 equations and i have....
5t+7r=823
t-r=137
and i tried to solve it but it didnt come out right. so i was wondering if someone could tell me the corrct equations or if they are right can you just tell me how you would do it. but if my equations are wrong you dont have to bother doing and showing me how you solved it. just tell me the correct equations. please help me!

[mausam]

The second equation (t-r=137) is wrong. The tape decks receipts will have 5 tapes and radios receipts will have 7 radios so (5t-7r=137)