Finding the Fourth Proportional to 139.42, 209.33 and 85.15

Step by Step Solution

1. Step 1: Write the proportion equation
   139.42 : 209.33 = 85.15 : x
2. Step 2: Convert to fraction form
   139.42/209.33 = 85.15/x
3. Step 3: Cross multiply
   139.42x = 209.33 × 85.15
4. Step 4: Simplify right side
   139.42x = 17,822.98
5. Step 5: Solve for x
   x = 17,822.98/139.42
6. Step 6: Final answer
   x = 127.84