Finding the Fourth Proportional to 10,856.20, 16,239.72 and 8,669.20

Step by Step Solution

1. Step 1: Write the proportion equation
   10,856.20 : 16,239.72 = 8,669.20 : x
2. Step 2: Convert to fraction form
   10,856.20/16,239.72 = 8,669.20/x
3. Step 3: Cross multiply
   10,856.20x = 16,239.72 × 8,669.20
4. Step 4: Simplify right side
   10,856.20x = 140,785,380.62
5. Step 5: Solve for x
   x = 140,785,380.62/10,856.20
6. Step 6: Final answer
   x = 12,968.20