There's no need for brackets except to alter the normal flow of BIDMAS/BODMAS.
Ie. 2 * 2 + 2 = 6
Bracketing it to (2 * 2) + 2 = 6
is horribly pointless, as it doesn't alter the end result, as it's still completed in the order you would have solved in anyway.
Changing the brackets to 2 * (2 + 2) = 8
DOES change the end result, so the brackets are necessary.
In your example: fielda = fieldb x fieldc - fieldd * 0.10 / fielde
Assuming b = 2, c = 3 etc
fielda = 2 * 3 - 4 * 0.1 / 5
= 5.92
Bracketing to: (fieldb * fieldc) - ((fieldd * 0.1) / fielde) isn't necessary as it still gives 5.92.
Only if you were changing it up to something like:
fieldb * (fieldc - fieldd) * (0.1 / fielde) would you need to bother
Which is -0.04 btw xD
These maths questions and the stupidity of most people on Facebook really get to me. It's the most basic thing in maths, and still people fuck it up.