In order to solve this problem, you need to subtract the metal sheet Tony already has (7m x 2m = 14m^2) from the total size he needs, which is 42m^2. So 42m-14m= 28m^2 that still need to be accounted for. Since it is a rectangular shape, one of the dimensions of the added sheet must be the same as the original. the only dimension would be 7m by 4m which would equal 28m^2. Add this to the original 14m^2 and this would add up to the desired 42m^2. So your answer is 7m by 4m sheet needs to be added.