Dave has a three-year college loan for $10,000. the lender charges a simple interest rate of 6 percent. how much interest will he have to pay? simple interest = p x r x t
and
joe borrowed $900 from sam for six months. how much will sam earn if he charges joe a simple interest rate of 4 percent? simple interest = p x r x t

1.If Dave has a three-year college loan for $10,000 and the lender charges a simple interest rate of 6 percent, Dave will have to pay $1,800 in interest. $10,000 principle at 6 percent annual interest rate is equal to a monthly interest payment of $50. 36 X $50 = $1,800.

2.If Joe borrowed $900 from Sam for six months and charges Joe a simple interest rate of 4 percent then Sam will earn $936.
good luck :) 

I'm gonna have to say about 13 percent