A bank loaned out $31,500, part of it at the rate of 13% annual interest, and the rest at 4% annual interest. The total interest earned for both loans was $2,610.00. How much was loaned at each rate?

a) $18,000 at 13%, $13,500 at 4%
b) $20,000 at 13%, $11,500 at 4%
c) $15,000 at 13%, $16,500 at 4%
d) $22,000 at 13%, $9,500 at 4%