For a given AP a 4 and d = 7. Then, the sum of its first 10 terms is A 350 B. 355 C. 74 D. 67

The sum of the first n terms of an arithmetic progression (AP) can be found using the formula:

S_n = n/2 * (2a + (n-1)d)

where: S_n is the sum of the first n terms, n is the number of terms, a is the first term, and d is the common difference.

Given in the problem, a = 4 and d = 7. We are asked to find the sum of the first 10 terms, so n = 10.

Substituting these values into the formula, we get:

S_10 = 10/2 * (2*4 + (10-1)*7) = 5 * (8 + 63) = 5 * 71 = 355

So, the sum of the first 10 terms of the given AP is 355. Therefore, the correct answer is B. 355.