Acar traveling at 46 mi/h slows to a speed of 23 mi/h in 5 seconds. it maintains that speed for 5 seconds and then slows to a stop after 5 more seconds. which graph shows the car’s speed over time?

For this case, the first thing you have to keep in mind is that we are in the presence of a piece function.
 We have then:
 For [0, 5]:
 A car traveling at 46 mi / h slows to a speed of 23 mi / h in 5 seconds.
 For [5, 10]:
 It maintains that speed for 5 seconds.
 For [10, 15]:
 then slows to a stop after 5 more seconds.
 In this case:
 x axis: represents time
 y axis: represents the speed.
 
 See attached image for the graphic v (t) vs t.