Answer:
3:4:7
Step-by-step explanation:
14-(3+4)
=14-7
=7
red:white:blue
3:4:7
Answer:
Where
and 
We are interested on this probability

And the best way to solve this problem is using the normal standard distribution and the z score given by:

If we apply this formula to our probability we got this:
And we can find this probability using the complement rule:

Step-by-step explanation:
Previous concepts
Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".
The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".
Solution to the problem
Let X the random variable that represent the variable of interest of a population, and for this case we know the distribution for X is given by:
Where
and 
We are interested on this probability

And the best way to solve this problem is using the normal standard distribution and the z score given by:

If we apply this formula to our probability we got this:
And we can find this probability using the complement rule:

21 divide by 4 is 5.25. She travels 5.25 miles per hour. 42 divide by 5.25 is 8. It would take 8 hours for Shelly to bike 42 miles.