The result is 42, right?Having been taught in Europe and then in the US, I grew up on metric and then had to convert to (ahem) British Imperial system. I can certainly vouch for how ridiculous that latter one really is in comparison.
But mathematical convention of operation precedence is a necessity in any complex mathematical treatment. Just imagine how complex and unreadable the following simple and elegant equation would be if you had to add parenthesis around every single operator: