What student loans to pay off first?

I have just under $20,000 in consolidated loans at a locked interest rate of 4.625%. I also have an additional $6,000 in private school loans at a 5.8% rate. Which should I work to pay off first? The larger one is aculating about 2.5 times as much in interest as the other, even though it is at a lower rate. Please help, and explain why with some math. Thanks!