Let Karen works x hours baby sitting So, she worked (18-x) hours giving music lessons So, According to question 5x + 12(18-x)=139 This gives 7*x=77 x=11 So, <span>Karen worked <em>11 hours baby sitting </em>and (18-11)=7 hours giving music lessons</span>
Options B, C and D have exactly 2 significant figures.
<u>EXPLANATION</u>
To see whether the numbers have exactly 2 significant figures, round all to 2 significant figures. The ones that remains the same have exactly 2 significant figures.