step 1
Find out the circumference
[tex]C=2\pi r[/tex]
where
r=10 cm
substitute
[tex]\begin{gathered} C=2\pi(10) \\ C=20\pi\text{ cm} \end{gathered}[/tex]
Remember that
The circumference subtends a central angle of 2pi radians
so
Applying proportion
Find out the central angle by an arc length of 40 cm
[tex]\begin{gathered} \frac{2\pi}{20\pi}=\frac{x}{40} \\ \\ x=4\text{ rad} \end{gathered}[/tex]
therefore
The answer is 4 radians Option B
