The cost of a college education has increased at a much faster rate than costs in general over the past twenty years. In order to compensate for this, many students work part- or full-time in addition to attending classes. At one university, it is believed that the average hours students work per week exceeds 20. To test this at a significance level of 0.05, a random sample of n = 20 students was selected and the following values were observed:

26 15 10 40
10 20 30 36
40 0 5 10
20 32 16 12
40 36 10 0

Based on these sample data, the critical value expressed in hours is?