Given a geometric progression (bn), the denominator of which is 4, and b1 = 3/4. Find the sum of its first four terms.

In the problem statement, it is said that the number one member of this sequence is 3/4, and the denominator of the geometric progression is 4.

Using the definition of a geometric progression, we find the second, third and fourth terms of this geometric progression.

Find the number that is in second place in this sequence:

b2 = b1 * q = (3/4) * 4 = 3.

We find the number that is in third place in this sequence:

b3 = b2 * q = 3 * 4 = 12.

We find the number that is in fourth place in this sequence:

b4 = b3 * q = 12 * 4 = 48.

We find the sum of the first four terms of this geometric progression:

b1 + b2 + b3 + b4 = 3/4 + 3 + 12 + 48 = 3/4 + 63 = 63 3/4.

Answer: The sum of the first four terms of this geometric progression is 63 3/4.