Solved
I can't read your worksheet, because it's in Prime 3.1 format, and the picture is clearly not the entire worksheet, but you can rewrite your final expression using the substitute keyword. Since r=w/wn, w=r*wn. So use the substitute keyword with w=r*wn. You can then use the substitute keyword again, with wn=(k/m)^1/2.
Edit. Actually, just change you second line to be w:=r*wn. Then the final line should evaluate the way you want.


