The product W has per unit contribution of $8$ with sold quantity of $124$ units, the product X has per unit contribution of $5$ with the sold quantity of $105$ units, product Y has per unit contribution of $9$ with sold quantity of $135$ units, product Z has per unit contribution of $12$ with sold quantity of $140$ units then the weighted average mean is A$.$ $$11\mathrm{.}75$ B$.$ $$10\mathrm{.}75.$ $$9\mathrm{.}75$ D$.$ $$8\mathrm{.}75$