area of two circles are in ratio 16 :81 find ratio of their circumference​

let radius of a circle be r₁ and other be r₂ 
so pi r₁²/pi r₂²=16/81
      r1/r2=4/9   
    2 pi r ₁/2 pi r ₂=2r₁/1r₂​=8/18=4/9