(i)Diameter of a cylindrical(closed) petrol tank=4.2 mRadius=24.2​=2.1 mHeight=4.5 mCurved Surface area=2πrh=2×722​×2.1×4.5=59.4sq.m(ii)Total surface area=2πr(r+h)=2×722​×2.1×(2.1+4.5)=2×722​×2.1×6.6=87.12 sq.mLet the amount of steel used in making the tank=xSteel wasted=12x​Given:Amount of steel required−Amount of steel wasted=T.S.A of the tank.⇒x−12x​=87.12⇒1212x−x​=87.12⇒1211x​=87.12⇒x=1112​×87.12=95.04sq.m∴95.04sq.m steel was used in actual while making such a tank.