B is 100 miles from A.  The traveler can walk at most 20 miles each day.

Inn #   d[i]    c[i]
 1       10      2
 2       13      5
 3       19      7
 4       22      3
 5       38      8
 6       42      6
 7       51      9
 8       65      5
 9       70      6
10       88      9
11      100      0 (home)