For example, if Jen has $20,000 to invest in two different accounts. One account earns 4% interest per year and the other earns 6% interest per year. If Jen wants to earn a total of $1,100 in interest per year, how much money should she invest in each account?

**Solution:**

Let x be the amount of money invested in the 4% account, and y be the amount of money invested in the 6% account.

The total amount invested is $20,000.

x + y = 20,000

The total interest earned is $1,100.

0.04x + 0.06y = 1,100

Therefore, the system of equations has two equations x + y = 20,000 and 0.04x + 0.06y = 1,100.