Finding the Fourth Proportional to 20,636.86, 28,479.45 and 12,139.60

Step by Step Solution

1. Step 1: Write the proportion equation
   20,636.86 : 28,479.45 = 12,139.60 : x
2. Step 2: Convert to fraction form
   20,636.86/28,479.45 = 12,139.60/x
3. Step 3: Cross multiply
   20,636.86x = 28,479.45 × 12,139.60
4. Step 4: Simplify right side
   20,636.86x = 345,729,131.22
5. Step 5: Solve for x
   x = 345,729,131.22/20,636.86
6. Step 6: Final answer
   x = 16,752.99