This problem uses the ideal gas law, PV = nRT. T for temperature must be in Kelvin, so we add 273.15 to the Celsius temperatures. We are then changing T from 303.15 K to 333.15K. The ratio of the temperatures 333.15/303.15 ~= 1.1. So holding pressure constant, the new volume of the balloon will be approximately 10% larger, or 330cm^3.