The answer to this question is 20.397. Group first the terms in the question (2x10) + (3x1/10) + (9x1/100) + (7x1/1000) then you'll get the answer of the the groups, 20 + 0.3 + 0.09 + 0.007 and lastly add it all up to get the final answer of 20.397. Hope this answers your question.