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.