Banyaknya cara pemilihan wakil kelas terdiri 3 anak untuk mengikuti rapat OSIS dari kelas yang mempunyai anggota 35 anak adalah...

The number of combinations of choosing $k$ items from a set of $n$ items is given by the formula:

$$C(n, k) = \binom{n}{k} = \frac{n!}{k!(n-k)!}$$

Here, $n = 35$ (total number of students) and $k = 3$ (number of students to be chosen).

$$C(35, 3) = \frac{35!}{3!(35-3)!}$$ $$C(35, 3) = \frac{35!}{3!32!}$$

$$C(35, 3) = \frac{35 \times 34 \times 33 \times 32!}{ (3 \times 2 \times 1) \times 32!}$$

Cancel out $32!$ from the numerator and denominator:

$$C(35, 3) = \frac{35 \times 34 \times 33}{3 \times 2 \times 1}$$ $$C(35, 3) = \frac{35 \times 34 \times 33}{6}$$

$$C(35, 3) = 35 \times \frac{34}{2} \times \frac{33}{3}$$ $$C(35, 3) = 35 \times 17 \times 11$$ $$C(35, 3) = 595 \times 11$$ $$C(35, 3) = 6545$$

The number of ways to choose 3 students from 35 is 6545.

Comparing this result with the given options:
A. 6.545
B. 11.456
C. 13.090
D. 39.270
E. 43.089

The calculated value matches option A.

The final answer is $\boxed{\text{A. 6.545}}$.