An investment club invested part of $8000 at 10% annual interest and the rest at 12%. If the annual income from these investments is $900, how much was invested at each rate?
a) $4000 at 10%, $4000 at 12%
b) $5000 at 10%, $3000 at 12%
c) $3000 at 10%, $5000 at 12%
d) $6000 at 10%, $2000 at 12%
