The total number of boys and girls enrolled in D is what percent of the total number of girls enrolled in A, C and E? (Correct to one decimal point)

We know that the ratio of the total number of Boys to Girls ratio is 7:5;
we also know that the total number of students is 2400.
Taking Boys and Girls to be 7x and 5x respectively, we get 12x = 2400, giving us x = 200
And hence, the total number of boys to be 1400 and the total number of girls to be 1000.

Next we're given that 15% of the boys are in section A, $$\frac{15}{100}\times\ 1400=210$$
And 22% of the girls are in section B, $$\frac{22}{100}\times\ 1000=220$$

Next, $$\frac{2}{7}$$ of the boys are in section B, $$\frac{2}{7}\times\ 1400\ =\ 400$$

We are also given that 500 boys are split between D and E in the ratio of 2:3, which would mean that D has 200 boys and E has 300 boys.
And the remaining boys are in Section C; the number of boys remaining are 290.

Next, we are given that 26% of the girls are in section D, that would mean that section d has 260 girls.
We are also given that section B has 120 girls.

The remaining girls must be split between section C and E, of which we know that C has 100 girls more than section E.
Taking the number of girls in section E to be x, we can calulculate these values as we know that 400 girls are yet to be place in any section,
giving us the equation $$2x+100=400$$
or simply $$x=150$$
which means that section E has 150 girls and Section C has 250 girls.

Our final data looks like this:
Section  Boys  Girls
A            210   220
B            400   120
C            290   250
D            200   260
E            300   150

Total number of boys and girls in section D is $$200+260=460$$
Total number of girls in A, C and E is $$220+250+150=620$$

The required percentage would be $$\frac{460}{620}\times\ 100=74.19$$%
Correcting this to one decimal place would give us 74.2%

Therefore, option A is the correct answer.