In the above solutions using Mid() and Left() the answer is being returned as a Text string. You will see that the result is left aligned, where as numbers are right aligned
Technically to convert it to a number you can either use a Value() function of perform some maths on it
eg:
=MID(B3,FIND("(",B3)+1,LEN(B3)-FIND("(",B3)-1)
Should be
=Value(MID(B3,FIND("(",B3)+1,LEN(B3)-FIND("(",B3)-1))
or
=- -MID(B3,FIND("(",B3)+1,LEN(B3)-FIND("(",B3)-1)
=Left(B3,FIND("(",B3)-1)
Should be
=Value(Left(B3,FIND("(",B3)-1))
or
=- - Left(B3,FIND("(",B3)-1)