Collin invested $5529 in the account paying 2% and $2171 in the account paying 9% interest.
Explanation:
Let x be amount invested at 2%
So, 7700 - x will be the amount invested at 9%
0.02(x) + 0.09(7800 - x) = 315
0.02x + 702 - 0.09x = 315
-0.07x = -387
x = $5529
7700 - x = 7700 - 5529
= $2171
Collin invested $5529 in the account paying 2% and $2171 in the account paying 9% interest.