Let the distance from the apartment bldg. to the car park = x
Let the distance from the car park to the office = 42-x
Since they take the same amount of time we have that
x / 60 + (42 - x) / 4 = x/ 40 + (42 - x) / 12 simplify
[4x + 60(42 - x)] / 240 = [12x + 40(42 - x) ] / 480
[4x + 2520 - 60x ] / 240 = [12x + 1680 - 40x ] / 480
[ 2520 - 56x] / 240 = [ 1680 - 28x] / 480
[2520 - 56x] / 240 = [ 840 - 14x ] / 240
2520 - 56x = 840 - 14x
1680 = 42x
x = 1680 / 42 = 40
So....the total time (in hours) =
40/60 + (42 - 40) / 4 =
2/3 hrs + 2/4 hrs =
2/3 hrs + 1/2 hrs =
40 mi + 30 min =
70 min =
7:10AM