Finding the Fourth Proportional to 21,688.35, 29,929.98 and 12,128.58

Step by Step Solution

1. Step 1: Write the proportion equation
   21,688.35 : 29,929.98 = 12,128.58 : x
2. Step 2: Convert to fraction form
   21,688.35/29,929.98 = 12,128.58/x
3. Step 3: Cross multiply
   21,688.35x = 29,929.98 × 12,128.58
4. Step 4: Simplify right side
   21,688.35x = 363,008,156.83
5. Step 5: Solve for x
   x = 363,008,156.83/21,688.35
6. Step 6: Final answer
   x = 16,737.47