Return on Investment

Hello Mr Moffit and open tuition team thanks for the good guidence, please help Its a question from one of MCQ, A division currently earns a ROI of 20%. Its considering investing in a project which has a residual income of $1000 at an inputed intrest of 20%.
what is the effect on divisions ROI if the project is undertaken?
A Increase
B Decrease
CRemain the same
D Not possible to tell from infomation

Soln: A answer- if divisions current ROI is 20% it could be representd by operating profit of 20000 and net assets of 100000. Residual income as operating profit -(net asset*intret which could be represented as 11000-(imputed intrest of 50000*20%
Therefore new roi would become existing operating profit+ projected operating profit) / (exisiting net assets+project net assets)=(20000+11000)/(100000+20000)=25.83an increase in ROI
Please sir help simplify this solution for me am strangling to get the idea where is he getting the numbers do we have to just think of numbers and substitute them in.
Aslo he goes on to say its quicker to realise if a Project is offering a positive residual income at an imputed intrest of 20% it must be offering a return higher than 20% therfore must improve the existing ROI of 20%. so what if it was giving a negative residual income does it mean that the ROI is falling so the divisin should reject the project, please can you help me with example for the above statement thank you.

Also advise me is operating profit the same as controllable profit?

my sol was like Current ROI assume profit of 40000/200000=20%(assummed net assets of 200000.
residual income assume proffit 40000-(0.2*) i got stuck on what asset figure to use.
appreciate all the advice and free guidence you give to the entire world thank you