[tex]\qquad\qquad\huge\underline{{\sf Answer}}♨[/tex]
As we know :
Length of arc = Radius × Angle made by Arc at center [ in radians ]
[tex]\qquad \tt \dashrightarrow \: arc = radius \times angle \: \: ( in \: \: rad)[/tex]
[tex]\qquad \tt \dashrightarrow \: arc = 8 \times \dfrac{ \pi}{2} [/tex]
[tex]\qquad \tt \dashrightarrow \: arc = 4 \pi \dfrac{ }{} \: \: units[/tex]
or
[tex]\qquad \tt \dashrightarrow \: arc = 4 \times 3.14 = 12.56 \: \: units\dfrac{ }{} \: \: [/tex]
