SOLUTION: Given Chicago is located at 42N and 88W and Detroit, MI is located at 42N and 83W. A driver leaves Chicago (42N, 88W) at 12pm and drives straight South at a speed of 70 miles per

1.  In this problem, the given coordinates of Detroit are IRRELEVANT and you can forget / (ignore) them - 

     it is EXCESSIVE and non-necessary data.



2.  In this problem, you can also forget about the fact that the Earth rotates about its axis (and about the Sun, too).



3.  The car moves straight South - it means that the car moves along the great circle of the Earthen sphere. 

    So, the distance from the starting point to the destination point is the arc of the great circle, which is

        Distance = Arc length = ,    (1)

    where R is the Earth radius (some mean, or average, value) and  is the angle in radians of the degree measure  (42° - 35°15’) = 6°45'.



4.  So, to solve the problem, you need

        - to convert 6°45' to radians;

        - to find from some source the Earth radius in miles;

        - then to calculate the distance (in miles) using formula (1);

        - then to divide the found distance by the given speed to get the time of how long the car moves;

        - then to add the found time to the reference time of 12 pm.