Finding the Fourth Proportional to 12,780.72, 17,639.64 and 7,478.28

Step by Step Solution

1. Step 1: Write the proportion equation
   12,780.72 : 17,639.64 = 7,478.28 : x
2. Step 2: Convert to fraction form
   12,780.72/17,639.64 = 7,478.28/x
3. Step 3: Cross multiply
   12,780.72x = 17,639.64 × 7,478.28
4. Step 4: Simplify right side
   12,780.72x = 131,914,167.02
5. Step 5: Solve for x
   x = 131,914,167.02/12,780.72
6. Step 6: Final answer
   x = 10,321.34