An investor invested a total of $3,500 in two mutual funds. One fund earned a 8% profit while the other earned a 5% profit. If the investor's total profit was $223, how much was invested in each mutual fund?

If $x was invested at 8% then the rest (3500-x) was at 5%.

So now just add up the two parts, and make sure it equals the total profit.
0.08x + 0.05(3500-x) = 223
Now finish it off