Answer: 0.0228
Step-by-step explanation:
Given : The mean and the standard deviation of finish times (in minutes) for this event are respectively as :-

If the distribution of finish times is approximately bell-shaped and symmetric, then it must be normally distributed.
Let X be the random variable that represents the finish times for this event.
z score : 

Now, the probability of runners who finish in under 19 minutes by using standard normal distribution table :-

Hence, the approximate proportion of runners who finish in under 19 minutes = 0.0228
Answer:
Answer is E hope this helps :)
Step-by-step explanation:
9t-6-6t=6 -- add 6 to both sides
9t-6t=12 -- combine like terms
3t=12 -- divide by 3
t=4