I create a text cell by changing a cell from type input to type text, and then type in that cell
I just tried what you said, and it gave me 2+2
Then "scrape" the mouse across the 2+2 to highlight the 2+2
Then either ctrl+shift+enter or click Evaluation on the menu bar and then click Evaluate in Place and the result is
I just tried what you said, and it gave me 4
Is that what you are looking for?