Let us take outer radius =R, inner radius =r, height =28 cm
Sum of both the curved surfaces of a hollow metallic cylinder =1408 cm2
∴2πRh+2πrh=1408
∴(R+r)=1408(28×2)÷(227)
∴(R+r)=8
Volume of metal =1408 cm3
⇒πR2h−πr2h=1408
⇒R2−r2=(140828)÷(227)
⇒(R+r)(R−r)=(140828)÷(227)
⇒(R+r)(R−r)=16
⇒(R−r)=2
Therefore, thickness of the metal in this cylinder =2 cm.