while calculating C for urea solution, why we did not took mass of solute 98g but 100g?

sir in this 5th video in last question you have taken w/m(no. of moles of solute) as x which you are saying is molality but as w/m ÷W should be molality that is (w/m÷1000)this whole term should be considered as molality not just w/m.. so we should be calculating it as: 0.02=molaity×18 , where, molaity =w/m÷1000 sir reply fast if i am right or wrong...

how this answer is calculated

what we did in 1st step and why not understood.please explain