let 'd' represent the distance in miles of the Boston Marathon, then we compute the distance per second in miles...

we use the following conversions:

hours to seconds:

1 hour * (60 minutes/1hour) * (60seconds/1minutes) = 3600 seconds

minutes to seconds:

1 minute = 60 seconds

we calculate distance per second:

(1 * 3600 + 18 * 60 + 27)/d

we now convert from a Marathon of 'd' distance to one of 30 miles:

30.*((1 * 3600 + 18 * 60 + 27)/d)

So the length of time, in seconds, it would take to complete a 30 mile race is:

30.*((1 * 3600 + 18 * 60 + 27)/d) seconds

or

(30./60.)*((1 * 3600 + 18 * 60 + 27)/d) minutes

or

(30./3600)*((1 * 3600 + 18 * 60 + 27)/d) hours