Finding the Fourth Proportional to 5,420.30, 8,120.72 and 5,128.70

Step by Step Solution

1. Step 1: Write the proportion equation
   5,420.30 : 8,120.72 = 5,128.70 : x
2. Step 2: Convert to fraction form
   5,420.30/8,120.72 = 5,128.70/x
3. Step 3: Cross multiply
   5,420.30x = 8,120.72 × 5,128.70
4. Step 4: Simplify right side
   5,420.30x = 41,648,736.66
5. Step 5: Solve for x
   x = 41,648,736.66/5,420.30
6. Step 6: Final answer
   x = 7,683.84