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An airplane flies from Portland to Seattle-Tacoma, a distance of 160 miles, at a constant speed of 240 miles per hour (4 miles per minute). The town of Mossyrock, Washington is on the flight path, halfway between the two airports. The function

\displaystyle {D}{\left({x}\right)}={4}{\left|{{x}-{20}}\right|}

gives the distance, in miles, of the airplane from Mossyrock t minutes after it takes off from Portland. You may graph the function with Desmos if it helps.

$\displaystyle {x}$	$\displaystyle {P}{\left({x}\right)}$
0	80
5	60
10	40
15	20
1	1
25	20
30	40
35	60
40	80

1. Choose the correct description of the domain and range.

The domain of $\displaystyle {D}{\left({x}\right)}$ is [0,40] because the plane is in the air for 40 minutes from Portland to Seattle.
The range of $\displaystyle {D}{\left({x}\right)}$ is [0,80] because the plane is never more than 80 miles from Mossyrock.
The domain of $\displaystyle {D}{\left({x}\right)}$ is [0,40] because the plane is in the air for 40 minutes.
The range of $\displaystyle {D}{\left({x}\right)}$ is [0,160] because the plane travels a total of 160 miles from Portland to Seattle.
The domain of $\displaystyle {D}{\left({x}\right)}$ is [0,20] because the plane passes Mossyrock after 20 minutes.
The range of $\displaystyle {D}{\left({x}\right)}$ is [0,80] because the plane is never more than 80 miles from Mossyrock.
The domain of $\displaystyle {D}{\left({x}\right)}$ is [0,20] because the plane passes Mossyrock after 20 minutes.
The range of $\displaystyle {D}{\left({x}\right)}$ is [0,160] because the plane travels a total of 160 miles from Portland to Seattle.

2. For what values of

\displaystyle {x}

\displaystyle {D}{\left({x}\right)}={20}

? (If there is more than one solution, separate them with a comma.)

3. For what values of

\displaystyle {x}

\displaystyle {D}{\left({x}\right)}<{20}

? (Give your answer using interval notation.)

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