Answer
5.
Lower limit: 0
Upper limit: 9
Work Step by Step
The -5 in the horizontal axis does not represent any class. 5 is the midpoint of the first class.
The class width is 10 and the midpoint of the first class is 5:
$Lower~limit~of~the~first~class=midpoint~of~the~first~class-\frac{class ~width}{2}=5-\frac{10}{2}=5-5=0$
$Upper~limit~of~the~first~class=midpoint~of~the~first~class+\frac{class ~width}{2}-1=5+\frac{10}{2}-1=5+5-1=9$
The second class lower limit is 10 (15-10/2). So, the upper limit of the first class must be 9. Otherwise the classes would overlap. Also, notice that the first class covers 10 different ages: 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.