now my baby 8 month old.birth weight 2.16 so what's avarage ideal weight now

A. 4 kg more than the birth weight should be there so 6.16 so since your child was born with low weight gain you can add about 4 kg on the minimum side by the age of eight months we expect the child should be at least 4 kg more than the ports on that basis if I say 6.16