Confidence Intervals

I'm really stumped on this question!

I've been asked to calculate the confidence intervals for the value of time calculated when the size is equal to : 3 time standard deviation.

Here is the data i've been given.

Time(h) Size(mm)
1 9.7
2 9.7
3 9.8
4 9.8
5 9.8
6 9.9
7 9.9
8 9.9
9 9.9
10 9.9
11 10.1
12 10.1
13 10.1
14 10.2
15 10.2
16 10.2
17 10.3
18 10.3
19 10.4
20 10.5

Any comments would be nice.
.