Roberta has $10,540 to invest. she plans to invest her money in certificates of deposit (cds) that have 2.1% interest, a stock portfolio that makes 2.5% interest, and a savings account that has 1.5% interest. she would like to make $231.69 in annual interest from her investments. also, to provide some risk security, she wants to invest a third of the amount she puts in the stock portfolio in the savings account. let x be the amount invested in cds, y be the amount invested in the stock portfolio, and z be the amount invested in the savings account. what is the amount roberta invests in each type of investment?