Finding the Fourth Proportional to 139.55, 209.34 and 78.71

Step by Step Solution

1. Step 1: Write the proportion equation
   139.55 : 209.34 = 78.71 : x
2. Step 2: Convert to fraction form
   139.55/209.34 = 78.71/x
3. Step 3: Cross multiply
   139.55x = 209.34 × 78.71
4. Step 4: Simplify right side
   139.55x = 16,476.10
5. Step 5: Solve for x
   x = 16,476.10/139.55
6. Step 6: Final answer
   x = 118.07