Question

Houses of three colours on a road

Answer 1

It's not really an equation to be solved.  You can set up some inequalities that describe the situation, e.g.:

b > r + y

y > r

3r > b

Then you can substitute and simplify, e.g. 3r > r + y or 2r > y

There would be a lot of possible solutions here.

 r=3, y=4, b=8 is one using small integers.