SE-SKOLORNAS 2011 Problem 4

Towns $A$ , $B$ and $C$ are connected with a telecommunications cable. If you for example want to send a message from $A$ to $B$ is assigned to either a direct line between $A$ and $B$ , or if necessary, a line via $C$ . There are $43$ lines between $A$ and $B$ , including those who go through $C$ , and $29$ lines between $B$ and $C$ , including those who go via $A$ . How many lines, are there between $A$ and $C$ (including those who go via $B$ )?