A train travels 75 feet in 1/13 second. At the same speed, how many feet will it travel in 5 1/2 seconds?

Use cross multiplication for direct proportions:

Given A:B, then C:X is given by
X=CB/A.

Here
75 ft : 1/13 sec.
X ft : 5 1/2 sec
we find X by:
X=75*5 1/2 ÷ 1/13
= 75*(11/2)÷(1/13)
=...