Finding the Fourth Proportional to 5,128.96, 7,078.72 and 3,139.20

Step by Step Solution

1. Step 1: Write the proportion equation
   5,128.96 : 7,078.72 = 3,139.20 : x
2. Step 2: Convert to fraction form
   5,128.96/7,078.72 = 3,139.20/x
3. Step 3: Cross multiply
   5,128.96x = 7,078.72 × 3,139.20
4. Step 4: Simplify right side
   5,128.96x = 22,221,517.82
5. Step 5: Solve for x
   x = 22,221,517.82/5,128.96
6. Step 6: Final answer
   x = 4,332.56