Finding the Fourth Proportional to 139.83, 209.89 and 85.86

Step by Step Solution

1. Step 1: Write the proportion equation
   139.83 : 209.89 = 85.86 : x
2. Step 2: Convert to fraction form
   139.83/209.89 = 85.86/x
3. Step 3: Cross multiply
   139.83x = 209.89 × 85.86
4. Step 4: Simplify right side
   139.83x = 18,021.26
5. Step 5: Solve for x
   x = 18,021.26/139.83
6. Step 6: Final answer
   x = 128.88