Please help solve this question! thank you!

3 3) Consider fusion reactor based on inertial confinement concept. It uses Elas=3 MJ laser to ignite solid D-T target (50%T+50%D) with the mass density p=0.2 g/cm' and the radius of R=0.5 mm. Find minimum of the laser efficiency, Nlas , to have positive net energy gain. Assume that each fusion D+T reaction gives Epr=17.5 MeV of energy and D-T fuel burns down completely. (20 points)