Finding the Fourth Proportional to 5,390.40, 7,429.04 and 3,990.72

Step by Step Solution

1. Step 1: Write the proportion equation
   5,390.40 : 7,429.04 = 3,990.72 : x
2. Step 2: Convert to fraction form
   5,390.40/7,429.04 = 3,990.72/x
3. Step 3: Cross multiply
   5,390.40x = 7,429.04 × 3,990.72
4. Step 4: Simplify right side
   5,390.40x = 29,647,218.51
5. Step 5: Solve for x
   x = 29,647,218.51/5,390.40
6. Step 6: Final answer
   x = 5,500.00