We know that the running times are normally distributed and that the time of a runner to qualify has to be in the fastest 16%. From the properties of the normal distribution, we know that:
• Between one and two standards deviation of the mean we have approximately 13.5% of the data.
,
• Between two and three standards deviations of the mean we have approximately 2.35% of the data.
,
• Above three standards deviations of the mean we have 0.15%.
This means that above one standard deviation there are approximately 16% of the data. Then we just need to add one standard deviation to the mean to find the time a runner needs.

Therefore, the running time to qualify is 66 min