Vector Image Representation on 640X480 Screen

Im trying to learn Computer Graphics. I have the following statement

For the representation of vector images, we assume that a typical image consists of 500 lines [BHS91]. Each line is deﬁned by its coordinates in the x direction and the y direction, and by an 8-bit attribute ﬁeld. Coordinates in the x direction require 10 bits (log 2 (640)), while coordinates in the y direction require 9 bits (log 2 (480)). Bits per line = 9bits + 10bits + 9bits + 10bits + 8bits = 46bits

I dont understand how Bits per line = 9bits + 10bits + 9bits + 10bits + 8bits = 46bits is calculated can someone explain with a little bit demonstration.

Each line is represented by its two endpoints plus the attribute field. Each endpoint has an $x$-coordinate and a $y$-coordinate. The $x$-coordinate requires $10$ bits while a $y$-coordinate requires $9$. So each point requires $10 + 9$ bits. The attribute field requires an extra $8$, so in total we have
$$(10 + 9) + (10 + 9) + 8 = 46$$