Please describe step by step for each part

On October 21, 2001, lan Ashpole of the United Kingdom achieved a record altitude of 3.35 km (11 000 ft) powered by 600 toy balloons filled with helium. Each filled balloon had a radius of about 0.50 m and an estimated mass of 0.30 kg (including the balloon and helium gas). (a) Estimate the total buoyant force on the 600 balloons. (10 points) (b) Estimate the net upward force on all 600 balloons. (10 points) . (c) Ashpole parachuted to Earth after the balloons began to burst at the high altitude and the system lost buoyancy. Why did the balloons burst? (5 points)