MathCad is solving incorrectly?

[NovaStark]

I am re-creating the appendix C of calculations to size a flare system, however I can't seem to get MathCad to correctly solve for my variable. I've swapped out units and values but I still don't get the correct answer.

I have uploaded the output from MathCad

However, the answer I am supposed to get is d=0.468 m. Not too sure how to make mathcad only give me the positive answer though.

[ValeryOchkov]

"Yes, it is, Harvey, and you are also right!"

Thank you!

[ValeryOchkov]

[ValeryOchkov]

Do you know why the second formula must be divided by two?
Author of the first Formula is onegreat scientist - Einstein (see above).
The authorship of the second formula is credited to two great scientists - Newton and Leibniz. Therefore, the second formula was divided by two, so that nobody was hurt.