Help: Analytical Chem Tritration Problem

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Can someone please help me with this back tritration problem!

a 100.0 ml sample of spring water was treated to convert any iron present to Fe2+ (AW 55.847) Addition of 25.00 ml of .002107 M K2Cr2O7 (FW294.185) resulted in the reaction:

6(Fe2+) + (Cr2O7)(2-) + 14H+ _____6(Fe3+) + 2(Cr3+) = 7H2O

the excess K2Cr2O7 was back titrated with 7.47 ml of .00979 M Fe2+ solution. Calculate the concentration (in ppm) of the iron in the sample (Recall: ppm Fe = #g Fe/10^6g sample).
 
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How many moles of Fe2+ are required to completely react given amount of dichromate?

How many were added during titration?

How many reacted in the first stage?