No 13.3813 + 0.1100 = 13.4913. (max. standard deviation)
13.4813 is less than max. standard deviation
First you multiply the two equations, equaling 3000000 kg and 60000 kg respectively. Once you have those numbers, you divide the Oakland mass by the Mapleville mass, so 3000000/60000. The answer is 50, to the tree is B, 50 times as big.
I'm not good with intigers, but if you added two negative intigers together wouldn't it still be negative? If you added -1 to -2 you'd get -3. It would always be less than the two original integers.