Question

find center mass of the system

Answer 1

This is an easy one.

Just go with the definition of center of mass (weighted means of position by mass)

So basically

CM y coordinate = (m(0)+m(a$\sqrt{3 }$/2)+m(0))/3m = a$\sqrt{3}$/6

CM x coordinate

CM x ordinate = (m(0)+m(a/2)+m(a))/3m = a/2

Hope this helped