Attach your worksheet, or at least a worksheet that shows the problem you have. NOT just a picture.
You're doing symbiolic evaluation. The symbolic processor does not handle units the way you might expect. It does not 'know' units, and treats them as unknown variables.
From the picture it seems that you've defined at least two variables, one with a unit 'ft' (blue, bold, italic), the other with a variable 'ft' (black, italic). If you relabel that variable ft to a unit ft, the symbolic processor will be smart enough to cancel the ft in denominator with the ft in the numerator of the result.
As stated the symbolic processor does not know about units. Sometimes it makes a wrong choice, apparently. I've modified the first occurence of this in your sheet on page 6.
You do the rest.
Nonetheless you may consider using numerical methods (solve block or the root command) for numerical results.
Here as an example the root command with its two flavours: