Finding the Fourth Proportional to 8,978.98, 12,390.36 and 5,621.64

Step by Step Solution

1. Step 1: Write the proportion equation
   8,978.98 : 12,390.36 = 5,621.64 : x
2. Step 2: Convert to fraction form
   8,978.98/12,390.36 = 5,621.64/x
3. Step 3: Cross multiply
   8,978.98x = 12,390.36 × 5,621.64
4. Step 4: Simplify right side
   8,978.98x = 69,654,143.39
5. Step 5: Solve for x
   x = 69,654,143.39/8,978.98
6. Step 6: Final answer
   x = 7,757.47