question:

http://i40.tinypic.com/2hwcswm.gif

solution:

$\displaystyle

\sigma=\frac{7.5\mu c}{14}=0.53571428571428571428571428571429\mu c\\

$

$\displaystyle

14=2\pi r\\

$

$\displaystyle

r=\frac{14}{\pi}\\

$

$\displaystyle

dq=\sigma r d\theta \\

$

$\displaystyle

k\sigma r\int_{0}^{\pi}d\theta=k\sigma r (\pi-0)=...

$

is it a correct solution?