an unknown gas diffuses 0.25 times as fast as helium gas (he). what is the molecular mass of the unknown gas? (atomic mass: he= 4 g)

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's. 

Ok so basically if you multiply that by the circumference then you get base times width times height which will equal out to be 7