Finding the Fourth Proportional to 139.89, 209.55 and 128.55

Step by Step Solution

1. Step 1: Write the proportion equation
   139.89 : 209.55 = 128.55 : x
2. Step 2: Convert to fraction form
   139.89/209.55 = 128.55/x
3. Step 3: Cross multiply
   139.89x = 209.55 × 128.55
4. Step 4: Simplify right side
   139.89x = 26,937.65
5. Step 5: Solve for x
   x = 26,937.65/139.89
6. Step 6: Final answer
   x = 192.56