Finding the Fourth Proportional to 21,105.72, 29,118.78 and 13,939.20

Step by Step Solution

1. Step 1: Write the proportion equation
   21,105.72 : 29,118.78 = 13,939.20 : x
2. Step 2: Convert to fraction form
   21,105.72/29,118.78 = 13,939.20/x
3. Step 3: Cross multiply
   21,105.72x = 29,118.78 × 13,939.20
4. Step 4: Simplify right side
   21,105.72x = 405,892,498.18
5. Step 5: Solve for x
   x = 405,892,498.18/21,105.72
6. Step 6: Final answer
   x = 19,231.40