Respuesta :
if the hole segment is 78 and some of it is 29 millimeters, you subtract 78-29= 49 which means segment AB is 49 millimeters
I am going to assume that B is between A and C.
AB + BC = AC segment addition postulate
AB + 29 = 78 substitution
AB = 49 subtraction property (subtracted 29)
Answer: 49 mm