The dimensions of an ellipse follow the pattern of a right triangle, except we have a2 = b2 + c2.
Here, a represents 1/2 the length of the major axis (or, the distance from the center to a vertex), b represents 1/2 the length of the minor axis (or, the distance from the center to a covertex), and c represents the distance from the center to a focus. Drawing a quick diagram will demonstrate that, at its apogee, Titan will be at a distance = a + c from Saturn: Titan--------------a--------------ctr-----c-----Saturn
a = 25,695 km. b = 24,627.5 km (25,695)2 = (24,627.5)2 + c2 c ~ 7,329 km
apogee distance from Titan to Saturn ~ 33,024 km