Finding the Fourth Proportional to 139.85, 209.59 and 71.31

Step by Step Solution

1. Step 1: Write the proportion equation
   139.85 : 209.59 = 71.31 : x
2. Step 2: Convert to fraction form
   139.85/209.59 = 71.31/x
3. Step 3: Cross multiply
   139.85x = 209.59 × 71.31
4. Step 4: Simplify right side
   139.85x = 14,945.51
5. Step 5: Solve for x
   x = 14,945.51/139.85
6. Step 6: Final answer
   x = 106.87