Two fourths is how pieces of the whole

At dinner, 2/5 of the people had fish and 1/3 had chicken. if everyone else had lamb, what fraction of the people had lamb? and if 40 people had lamb , calculate the total number of people at the dinner.

Quick translate "x is 12 units from 20" into an equation. what are the values of x being described? if you can answer any of my other questions that'd be great too

Factor the polynomial by its greatest common monomial factor.