We just use the distance formula: For lines, YA and AB, draw a diagram and label all the points!
Thus, we have √102−82=√100−64=√36=6 feet.
Similarly, we do it for XA and XB, and since this is 17 feet, we get √172−82=√289−64=√225=15 feet.
Thus, the answer is 6+15=21 feet.