At the rice processing plant, 750 kg of rice containing 320 ppb total arsenic was thoroughly mixed with 250 kg of rice containing 480 ppb of total

At the rice processing plant, 750 kg of rice containing 320 ppb total arsenic was thoroughly mixed with 250 kg of rice containing 480 ppb of total arsenic. The rice was loaded into 1-kg bags? What is the concentration of total arsenic in a bag? ___________ ppb. Assume all the numbers are known to 3 digits. The answer has to be somewhere ___________ 320 and 480 ppb