An investor has a total of $15,000 to invest in two different accounts. One account pays an annual simple interest rate of 4%, and the other account pays an annual simple interest rate of 6%. At the end of one year, the investor earned a total of $780 in interest from both accounts. Which of the following systems of linear equations represents this situation, if represents the amount invested in the 4% account and represents the amount invested in the 6% account?
x + y = 15000
0.04x + 0.06y = 780
x + y = 780
0.04x + 0.06y = 15000
x + y = 15000
4x + 6y = 780
0.04x + 0.06y = 15000
x + y = 780
