Finding the Fourth Proportional to 21,408, 29,543.06 and 11,978.79

Step by Step Solution

1. Step 1: Write the proportion equation
   21,408 : 29,543.06 = 11,978.79 : x
2. Step 2: Convert to fraction form
   21,408/29,543.06 = 11,978.79/x
3. Step 3: Cross multiply
   21,408x = 29,543.06 × 11,978.79
4. Step 4: Simplify right side
   21,408x = 353,890,051.80
5. Step 5: Solve for x
   x = 353,890,051.80/21,408
6. Step 6: Final answer
   x = 16,530.74