The fourth term of the arithmetic progression is 3. Find the sum of the first seven terms of the progression.

Any member of the arithmetic progression can be represented as:

an = a1 + d * (n – 1), where n is the ordinal number of a member of the progression, and d is the difference of the progression.

The fourth term of the progression, according to the problem statement, is 3. Therefore, we can write the equation:

a4 = a1 + d * (4 – 1) = a1 + 3 * d = 3.

The sum S of the first 7 members of the arithmetic progression can be calculated by the formula:

S = (a1 + a7) * 7/2 = (a1 + a1 + 6 * d) * 7/2 = (2 * a1 + 6 * d) * 7/2 = 2 * (a1 + 3 * d) * 7/2 = 7 * (a1 + 3 * d) = 7 * a4 = 7 * 3 = 21.

Answer: 21.