depth of welding in a spot pulsed laser welding of aluminum plates

Question

In spot pulsed laser welding of aluminum plates (density=2700kg/m³, specific heat=896J/kg, melting temp-939K, latent heat of melting – 398 kJ/kg) at a temp of 20⁰C, pulse with energy of 0.5J is focused onto an area of 0.05mm². if the entire energy is coupled into the material, what will be the depth of weld assuming the CS area of the weld is circular and is uniform throughout its depth and only heat conduction in the direction of penetration                                                                                             

(a) 5.34mm                                    (b) 2.5mm

(c) 4.23mm                                    (d) 3.85mm