Which of the following equations can be used to calculate the values of t for which the distance between chris and any is 300 miles

The first thing we must know in this case is that the distance is equal to the speed for time.
 We have then:
 For Chris:
 d1 = 40 * t
 For Amy:
 d2 = 60 * (t-2)
 The distance between both will be given by the hypotenuse of the rectangle triangle:
 300 = root ((40 * t) ^ 2 + (60 * (t-2)) ^ 2)
 
 300 = root ((40 * t) ^ 2 + (60 * (t-2)) ^ 2) 
 option 3