Solve floor(r) + r = 12.2 - r.
We have \(\lfloor r \rfloor = 12.2 - 2r\). Then 12.2 - 2r must be an integer. Then \(r = k + 0.1\text{ or }r = k + 0.6\) for some integer k. Now you can substitute that and try to solve it like a linear equation.
