Finding the Fourth Proportional to 139.38, 209.16 and 78.56

Step by Step Solution

1. Step 1: Write the proportion equation
   139.38 : 209.16 = 78.56 : x
2. Step 2: Convert to fraction form
   139.38/209.16 = 78.56/x
3. Step 3: Cross multiply
   139.38x = 209.16 × 78.56
4. Step 4: Simplify right side
   139.38x = 16,431.61
5. Step 5: Solve for x
   x = 16,431.61/139.38
6. Step 6: Final answer
   x = 117.89