Answer:
Mass can never be negative. Everything has mass. Just like how they ask you to find area under the graph in maths. If the area is in the 3rd and 4th quadrant, when calculated, you would get negative answer.However, area can not be negative because it is a place/ location. It's exactly the same as mass.
Originally there must been
1,4775E6 + 2.25E4 = 147.75E4 + 2.25E4 = 150E4 present at start
% = 2.25 / 150 = 1.5 % of 235 U left
according to the facts it should be a numerous amount of wrong answers so ignore dis