Karen makes $5 per hour baby-sitting and $12 per hour giving music lessons. One weekend, she worked a total of 18 hours and made $139. How many hours did she spend baby-sitting?
Let Karen works x hours baby sitting
So, she worked (18-x) hours giving music lessons
According to question
5x + 12(18-x)=139
Karen worked 11 hours baby sitting and (18-11)=7 hours giving music lessons