Let "x" stand for the amount invested at 12%.
That means the amount invested at 10% must be 27,000 - x
So, the total return must be x (the amount invested at 12%) times 0.12 plus the amount invested at 10% (27,000 - x) times 0.10. In algebraic terms:
Total return = .12*x + .1*(27,000 - x) = 2,990
Multiply out the expression above:
.12x + 2,700 - .1x = 2,990
Combine like terms:
.02x + 2,700 = 2,990
Subtract 2,700 from both sides:
.02x = 290
Divide both sides by .02:
x = 14,500
So you would invest $14,500 at 12% and 12,500 at 10%.