AMC8 2008 Problem 13

Mr. Harman needs to know the combined weight in pounds of three boxes he wants to mail. However, the only available scale is not accurate for weights less than 100 pounds or more than 150 pounds. So the boxes are weighed in pairs in every possible way. The results are 122,125 and 127 pounds. What is the combined weight in pounds of the three boxes?
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Answer Choices
A. 160
B. 170
C. 187
D. 195
E. 354