Given the following activity network: A$2$ A$1$ Ki A$3$ Activity Al takes $5$ weeks. A$2$ takes $7$ weeks, and A$3$ takes $4$ weeks with a $50\%$ probability and $10$ weeks with a $50\%$ probability. What is the project completion time under the worst$-$case scenario, that is$.$ A$3$ is late and takes $10$ weeks? a$.12$ weeks b$.9$ weeks C$.10$ weeks d$.15$ weeks