for checking the quality level of a wallpaper hanging job, a random area of $300$ m$2$ is taken and no$.$ of blemisher are count. the total no$.$ of blemishes for $30$ such samples are $80.$ The $3$Sigma control limits are an appropriate chart are

a$)-5\mathrm{.}534$ and $10\mathrm{.}668$

b$)0$ and $10\mathrm{.}668$

c$)-2\mathrm{.}232$ and $7\mathrm{.}566$

d$)0$ and $7\mathrm{.}566$