Jackie invested money in two different accounts, one of that earned 12% interest per year and another that earned 15% interest per year. The amount invested at 15% was 100 more than twice the amount at 12%. How much was invested at 12% if the total annual interest earned was $855?

Let x = the amount invested at 12% interest. Let y = the amount invested at 15% interest. Since the amount invested at 15% is 100 more then double the amount at 12%, then y = 2x + 100. Since the total interest was $855, use the equation 0.12x + 0.15y = 855. You have two equations with two variables. Use the second equation 0.12x + 0.15y = 855 and substitute (2x + 100) for y: 0.12x + 0.15(2x + 100) = 855. Use the distributive property: 0.12x + 0.3x + 15 = 855. Combine like terms: 0.42x + 15 = 855. Subtract 15 from both sides: 0.42x + 15 - 15 = 855 - 15; simplify: 0.42x = 840. Divide both sides by 0.42: 0.42x/0.42= 840/0.42.
Thus, x = $2,000, which is the amount invested at 12% interest.