K18

a) d=2r=2\cdot4{,}0cm=8{,}0cm
b)
V=Ah
V=\pi\cdot4^2\cdot8
V=128\pi\ cm\ \approx402.123...\approx400cm^2
c)
\tan\alpha=\frac{4}{8}=26{,}565...°\approx26{,}6°