Finding the Fourth Proportional to 139.37, 209.15 and 78.62

Step by Step Solution

1. Step 1: Write the proportion equation
   139.37 : 209.15 = 78.62 : x
2. Step 2: Convert to fraction form
   139.37/209.15 = 78.62/x
3. Step 3: Cross multiply
   139.37x = 209.15 × 78.62
4. Step 4: Simplify right side
   139.37x = 16,442.98
5. Step 5: Solve for x
   x = 16,442.98/139.37
6. Step 6: Final answer
   x = 117.98