Minus is more or less interchangeable with negative in these cases, but negative should definitely be accepted, and should be used in more formal settings.
Minus six times ten is minus sixty.This should be accepted too.
As a native english speaker , I've never heard anyone say negative six , it should be minus 6 x 10 is ( or equals = ) minus 60
------ hey duo ! you need to show the math , too . . .
-6 x 10 = -60
Big 15 aug 21 celebrating szent istva'n nap itt san franciscoban . . .
Szent István nap? You are 5 days too early. :P (It is on August 20)
alan.asquith is right ... "negative six" is definitely an American English usage, and would raise eyebrows (though would probably be understood in most cases) in the UK. "minus six" is the correct UK English usage, not "negative six"