Answer:
....there are several ways to calculate AC :
1) pythagoras
AC²=AD²+DC²
AC²= 80²+50²
AC =V8900=94.339...=94m
remove 15 of the circle's diameter, as you'll have to go around the semicircle.
half-circle length:(pi*15)/2 = 23.55m
passing through AC: length = 94-15+23.55=102.55m
2) AB+BC or AD+AC (same dimension)=
AB+AC = 80+50=130m
the shortest distance is the one through the semicircle
Explanation: