Question

(5,?) is on the line x + 3 = y. Find the other half of the coordinate.

Answer 1

You are given point (5, ?), and we need to solve for "?" aka y-coordinate.
You have x-coordinate of 5, so plug in x=5;

x + 3 = y
(5) + 3 = y
8 = y

So y-coordinate is 8.