Karen make $5 per hour babysitting and $12 per hour giving music lessons. On the weekend, she worked a total of 18 hours and made $139. How many HOURS did she spend BABYSITTING

11 hours

Step-by-step explanation:

Let's say Karen makes x hours babysitting and y hours giving music lessons.

Because she worked a total of 18 hours, we know that x + y = 18.

5 * x is how much money she earns babysitting for x hours, while 12 * y is how much money she earns giving music lessons for y hours. Adding them up gives her total revenue:

5x + 12y = 139

We now have a system of equations. Let's multiply both sides of x + y = 18 by 12:

12 * (x + y) = 18 * 12

12x + 12y = 216

Now, subtract 5x + 12y = 139 from 12x + 12y = 216:

     12x + 12y = 216

-     5x + 12y = 139

       7x + 0y = 77

Divide both sides by 7:

x = 11

Thus, Karen spent 11 hours babysitting.