Residual Income and Return of Investment

Hi, I need some help with the below question which was in the June 2012 exam paper.

“An investment centre earns a ROI of 18% and a residual income (RI) of £300,000. The cost of capital is 15%. A new project offers a return on capital employed 17%.

If the new project were adopted, what would happen to the investment centre’s return on investment and RI?

Return on Investment: Increase or Decrease?
Residual Income: Increase or Decrease?”

The answer is ROI Decreases and RI increases but i am having trouble understanding how.

It is my knowledge that Return of Capital Employed is the same as Return of Investment so 17%-18% = -1% so ROI decreases.

But having great difficulty understanding how RI increases.

Thanks