The sum of the difference between the expenditurers in july and August on items C and that of F as a percentage of the change in total expenditure between the two months is

Amount Spent on C in July = $$\frac{45}{360}$$ of Total expense i.e. $$\frac{45}{360}\times\ 27000\ =\ 3375$$.
Amount spent on F in July = $$\frac{45}{360}\times\ 27000\ =\ 3375$$.
Amount spent on C in August = $$\frac{36}{360}\times\ 30000\ =\ 3000$$.
Amount spent on F in August = $$\frac{54}{360}\times\ 30000=4500$$.
Difference in expenditures of C = |3375 - 3000| = 375 
Difference in expenditures of F = |4500 - 3375| = 1125
Sum of differences = 1500 and Total change in expenditures for the 2 months = 30000 - 27000 = 3000.
Now, percentage of Sum of differences on Total change = $$\frac{1500}{3000}\times\ 100\ =\ 50\%$$.