Convert units word problems (metric)

Solve word problems that involve converting between metric measures of distance, volume, and mass, as well as measures of time.
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Problem

James has 14, comma, 500, space, g of sand in his sandbox. He brings home another 7, comma, 400, space, g of sand from the beach to add to his sandbox.
How many kilograms of sand does James have in his sandbox now?
k, g