Finding the Fourth Proportional to 7,128.72, 10,685.52 and 3,428.64

Step by Step Solution

1. Step 1: Write the proportion equation
   7,128.72 : 10,685.52 = 3,428.64 : x
2. Step 2: Convert to fraction form
   7,128.72/10,685.52 = 3,428.64/x
3. Step 3: Cross multiply
   7,128.72x = 10,685.52 × 3,428.64
4. Step 4: Simplify right side
   7,128.72x = 36,636,801.29
5. Step 5: Solve for x
   x = 36,636,801.29/7,128.72
6. Step 6: Final answer
   x = 5,139.32