Finding the Fourth Proportional to 3,990.80, 5,431.52 and 3,990.80

Step by Step Solution

1. Step 1: Write the proportion equation
   3,990.80 : 5,431.52 = 3,990.80 : x
2. Step 2: Convert to fraction form
   3,990.80/5,431.52 = 3,990.80/x
3. Step 3: Cross multiply
   3,990.80x = 5,431.52 × 3,990.80
4. Step 4: Simplify right side
   3,990.80x = 21,676,110.02
5. Step 5: Solve for x
   x = 21,676,110.02/3,990.80
6. Step 6: Final answer
   x = 5,431.52