Finding the Fourth Proportional to 21,128.88, 31,724.37 and 11,787.15

Step by Step Solution

1. Step 1: Write the proportion equation
   21,128.88 : 31,724.37 = 11,787.15 : x
2. Step 2: Convert to fraction form
   21,128.88/31,724.37 = 11,787.15/x
3. Step 3: Cross multiply
   21,128.88x = 31,724.37 × 11,787.15
4. Step 4: Simplify right side
   21,128.88x = 373,939,907.85
5. Step 5: Solve for x
   x = 373,939,907.85/21,128.88
6. Step 6: Final answer
   x = 17,698.05