Question

a line connecting (5, 6) to another point has an undefined slope. What is the closest point on this line with whole number coordinates below (5, 6)?

Answer 1

Lets do it like this:
As this is a line connecting to another point that has an undefined slope, X is 5 for all values of Y: 
Then 
P1(5,6) 
P2(5,7). 
P3(5,8).

I hope this can help you