Compared to January, the total expenditure on carnations in March

Total population = 70000

Average consumer expenditure on Roses and carnations = 47.4

Total expenditure on both carnations and roses = 47.4*70000

                                                                       = 3318000

Given total expenditure on roses = 1136916

So the total expenditure on carnations = 3318000 - 1136916

                                                           = 2181084

Similarly in the month of March 

Average consumer expenditure on Roses and carnations = 49.5

Total expenditure on both carnations and roses = 49.5 *70000

                                                                       = 3465000

Given total expenditure on roses = 1137915

So the total expenditure on carnations = 3465000 - 1137915

                                                           = 2327085

Percentage increase in Expenditure  = (2327085-2181084)/2181084

=6.69%

Hence C is the correct answer