A large organisation promotes its call centre efficiency stating that the average time to answer all calls is $7\mathrm{.}5$ minutes with a standard deviation of $2\mathrm{.}4$ minutes. Assuming the waiting time duration is approximately normal: c$.$ What is the waiting time that the associated with the top $10\%$ of customers $$ i$.$e$.$ if you are unlucky enough to be a customer who is subjected to the $10\%$ of longest waiting times.