Finding the Fourth Proportional to 12,931.20, 19,401.60 and 5,145.60

Step by Step Solution

1. Step 1: Write the proportion equation
   12,931.20 : 19,401.60 = 5,145.60 : x
2. Step 2: Convert to fraction form
   12,931.20/19,401.60 = 5,145.60/x
3. Step 3: Cross multiply
   12,931.20x = 19,401.60 × 5,145.60
4. Step 4: Simplify right side
   12,931.20x = 99,832,872.96
5. Step 5: Solve for x
   x = 99,832,872.96/12,931.20
6. Step 6: Final answer
   x = 7,720.31