Finding the Fourth Proportional to 20,687.76, 31,031.28 and 5,105.40

Step by Step Solution

1. Step 1: Write the proportion equation
   20,687.76 : 31,031.28 = 5,105.40 : x
2. Step 2: Convert to fraction form
   20,687.76/31,031.28 = 5,105.40/x
3. Step 3: Cross multiply
   20,687.76x = 31,031.28 × 5,105.40
4. Step 4: Simplify right side
   20,687.76x = 158,427,096.91
5. Step 5: Solve for x
   x = 158,427,096.91/20,687.76
6. Step 6: Final answer
   x = 7,658.01