Finding the Fourth Proportional to 128.40, 192.69 and 56.31

Step by Step Solution

1. Step 1: Write the proportion equation
   128.40 : 192.69 = 56.31 : x
2. Step 2: Convert to fraction form
   128.40/192.69 = 56.31/x
3. Step 3: Cross multiply
   128.40x = 192.69 × 56.31
4. Step 4: Simplify right side
   128.40x = 10,850.37
5. Step 5: Solve for x
   x = 10,850.37/128.40
6. Step 6: Final answer
   x = 84.50