you were correct throughout, but you made the slope negative in the denominator and numerator, making it positive . using what you said at first for the variables you would get the points (77,25) and (68,20).
using slope formula you get:
giving you a slope of
next i would use point slope form at first then rearrange,so..
using the point (68,20)
now to find when they are the same.to do this set y=x
so at -40 degrees they are the same