A diagram of an ellipse is shown below
VW is the major axis
ST is the minor axis
P is a point on the ellipse
A and B are the foci (or focus)
The length of major axis is given by either VA+AW or AP+BP
One useful fact to know that AP+BP is constant wherever the point P is on the ellipse
We know that the distance of the point 'P' from one focus is 11 units and from the other focus is 7 units, so we know the length of AP and BP.
Hence, the length of major axis is 11+7=18 units
