It’s c. Where the two planes intersect
Answer: second option.
Step-by-step explanation:
You must apply 
Then, given the right triangle and the angle D, the opposite side and the hypotenuse of the triangle are the following:

Therefore, when you substitute values, you have:

Reduce the fraction, then you obtain:

7k/3 = 21
x 3 x3
7k = 63
/7 /7
k = 9
(7(9)/3 = 21 = 63/3 = 21 = 21 = 21)
Answer:
It travels for 1 hour, then stops for 1 hour, and finally travels again for 3 hours.
Step-by-step explanation:
Distance changes over the first hour of travel, but then doesn't change for one hour, and then it continues on for the next three hours