Question 970173
in school they probably want you to start with 60 mi/hr × 1 hr/60 min and cross out the alike units each time making a really long fraction and multiplying the tops seperate from the bottom then simplifying. 
But a really simple way to deal with fraction conversions is to replace them each with what they are equal to and simplify. It can't be done in 1 step but the units are already done so tell me what you think


60 mph = 60 miles/60 min = 1 mile per minute
1 mile/ 1 min = 5280 feet/ 60 seconds = 88 feet/sec

anyway it takes 5 seconds to enter the tunnel and is passing 88 feet of itself through at each second so 5sec* 88 feet/sec = 440 feet 

So almost 10 boxcars which makes sense if anyone is wondering. 

the length of the tunnel is... 
If you are thinking it is a trick question and the front is already 5 seconds or 440 feet into the tunnel and you have to add that to 40 seconds you are actually overthinking the problem. The back or the front of the train can be used as a marker. the back enters at the begining of 40 seconds and exits the tunnel after 40 seconds passes. The front enters the tunnel at the begining of 5 seconds and exits 5 seconds before the whole train exits or at 35 seconds or 5 seconds before 40. 
Anyway the tunnel is 40 seconds long. 
40 sec * 88 feet/sec = 3520 feet long