The difference between city hall and the post office is 6 1/2 miles ( six and one half)city hall is 1 1/3 (one and one fourth not eleven)miles closer to the library site than it is to the post office. let d represent the distant from city hall to the library site write an expression for the distance from the library site to the post office

City hall to post office = 6 1/2 miles  = represented by f
city hall to library site = 1 1/4 miles  = represented by d
library site to post office = unknown. = represented by e

City hall to library site  PLUS library site to post office IS EQUAL to city hall to post office

d + e = f

1 1/4 + e = 6 1/2

find e.
e = 6 1/2 - 1 1/4
e = 13/2 - 5/4
e = (13*2)/(2*2)  - 5/4
e= 26/4 - 5/4
e = (26-5)/4
e = 21/4
e = 5 1/4    distance from library site to post office.
 
To check:
d + e = f

1 1/4 + e = 6 1/2
1 1/4 + 5 1/4 = 6 1/2
6 2/4 = 6 1/2
6 1/2 = 6 1/2