Explanation

To find the fourth proportional of 3, 7, and 15:

Let's denote the fourth proportional as x. We set up the proportion:

3/7 = 15/x

Step 1: Cross-multiply.

3x = 7 × 15

Step 2: Calculate the product of 7 and 15.

3x = 105

Step 3: Solve for x.

x = 105 / 3

x = 35