What is the expected boiling point elevation of water for a solution that contains 189g of sodium chloride dissolved in 1.0 kg of water?

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?