Finding the Fourth Proportional to 20,689.06, 30,978.50 and 14,128.06

Step by Step Solution

1. Step 1: Write the proportion equation
   20,689.06 : 30,978.50 = 14,128.06 : x
2. Step 2: Convert to fraction form
   20,689.06/30,978.50 = 14,128.06/x
3. Step 3: Cross multiply
   20,689.06x = 30,978.50 × 14,128.06
4. Step 4: Simplify right side
   20,689.06x = 437,666,106.71
5. Step 5: Solve for x
   x = 437,666,106.71/20,689.06
6. Step 6: Final answer
   x = 21,154.47