Finding the Fourth Proportional to 21,078.56, 31,617.12 and 9,990.56

Step by Step Solution

1. Step 1: Write the proportion equation
   21,078.56 : 31,617.12 = 9,990.56 : x
2. Step 2: Convert to fraction form
   21,078.56/31,617.12 = 9,990.56/x
3. Step 3: Cross multiply
   21,078.56x = 31,617.12 × 9,990.56
4. Step 4: Simplify right side
   21,078.56x = 315,872,734.39
5. Step 5: Solve for x
   x = 315,872,734.39/21,078.56
6. Step 6: Final answer
   x = 14,985.50