Finding the Fourth Proportional to 9,980.78, 13,772.84 and 5,728.85

Step by Step Solution

1. Step 1: Write the proportion equation
   9,980.78 : 13,772.84 = 5,728.85 : x
2. Step 2: Convert to fraction form
   9,980.78/13,772.84 = 5,728.85/x
3. Step 3: Cross multiply
   9,980.78x = 13,772.84 × 5,728.85
4. Step 4: Simplify right side
   9,980.78x = 78,902,534.43
5. Step 5: Solve for x
   x = 78,902,534.43/9,980.78
6. Step 6: Final answer
   x = 7,905.45