In Big C retail outlet, the last week record showed that out of $1000$ mobile phones sold in which $85$ were Vivo brand whereas the same branded mobile phones were as $120$ out of $500$ mobile phones sold in the current week. It is interested to test whether the current proportion of sales is more than that of previous week.

a$)$ Set null and alternate hypotheses

b$)$ Carry out the test using $1\%$ level of significance.