Six solid hemispherical balls have to arranged one upon the other vertically .Find the minimum total surface area of the cylinder in which the hemispherical balls can be arranged, if the radii of each hemispherical ball is $7$ cm.
$a.)2056\\ \color{green}{b.)2156}\\ c.)1232\\ d.)\text{none of these}\\$
I tried
$h=7\times 6=42$ cm
$r=\dfrac{7}{2}$ cm
$\text{Total surface area }=2\pi\times \dfrac72\times 42+2\times \pi\times \left(\dfrac72\right)^2\approx 1000.5\quad cm^2$
But the book is giving option $b.)$