The weight of topsoil sold in a week is normally distributed with a mean of $800$ tons and a standard deviation of $80$ tons.

$($a$)$ What percentage of weeks will sales exceed $960$ tons? $($Round your answer to two decimal places.$)$

$\%$

$($b$)$ What percentage of weeks will sales be less than $720$ tons? $($Round your answer to two decimal places.$)$

$\%$

$($c$)$ What percentage of weeks will sales be between $720$ and $960$ tons? $($Round your answer to two decimal places.$)$