Finding the Fourth Proportional to 139.72, 209.58 and 71.28

Step by Step Solution

1. Step 1: Write the proportion equation
   139.72 : 209.58 = 71.28 : x
2. Step 2: Convert to fraction form
   139.72/209.58 = 71.28/x
3. Step 3: Cross multiply
   139.72x = 209.58 × 71.28
4. Step 4: Simplify right side
   139.72x = 14,938.86
5. Step 5: Solve for x
   x = 14,938.86/139.72
6. Step 6: Final answer
   x = 106.92