Question 865055
You start with 63. This is given. The class width is 5. This is also given. So the first interval will go from 63 to 68 (since 63+5 = 68 or 68-63 = 5). 


The second interval will start at the next integer up, which is 69. You'll add 5 to this to get 69+5=74. 


The third interval will start at the next whole number above 74, which is 74+1 = 75. We can stop here, but we might as well construct the rest of the interval. This interval ends at 75+5 = 80. 



Summary of what we found:


First Interval: 63-68
Second Interval: 69-74
Third Interval: <font color="red">75</font>-80



So the lower limit of the third class is <font size=4 color="red">75</font>