Finding the Fourth Proportional to 139.91, 209.59 and 128.43

Step by Step Solution

1. Step 1: Write the proportion equation
   139.91 : 209.59 = 128.43 : x
2. Step 2: Convert to fraction form
   139.91/209.59 = 128.43/x
3. Step 3: Cross multiply
   139.91x = 209.59 × 128.43
4. Step 4: Simplify right side
   139.91x = 26,917.00
5. Step 5: Solve for x
   x = 26,917.00/139.91
6. Step 6: Final answer
   x = 192.39