1 i have no clue how to do.. other somehwat...

first one...

2 student loans totalin 10,000.. he borrwed the max allowed at 7% simple interest and the remainder at 8.25% simple interest. After 1 year he owed 725 in interest.. how much did he borrow @ each interest rate

first i did 10,000 x .07 = 700

then 10,000 x .0825 = 825... but i dont know what to do, i dont think i did that step right

second problem

owned of video store sells 96 blank tapes per week if he charges 6 per tape. for every .50 he increases the price, he sells 4 fewer tapes per week.

i have to write equations for price / # of tapes / revenue

so woulnd't price = 6 + .5x

tape = 96 - 4x

revenue = (6 + .5x)(96 - 4x)

how mcuh should he charge for a tape in order to make a revunue of 630 per week from the tapes

any help is appreciated or point me in the right direction... thank you again!