You could use the equation y=mx+b
Find the slope of the two coordinates. I would personally suggest using stack and subtract:
(0,2)     2-5      -3       3
(2,5)    -------= ------= -----
             0-2     -2       2
We have the slope but we need to find the y-intercept.
y=3
    --x+b
    2
Plug one of the coordinates in the constructed equation above:
2=3
    -- (0)+b
     2
2=0+b
-0=-0
------------
b=2
We found the slope and y-intercept. Now we have our complete equation. The equation is:
y=3
    --x+2
    2
Have a blessed day!