Finding the Fourth Proportional to 139.62, 209.25 and 78.78

Step by Step Solution

1. Step 1: Write the proportion equation
   139.62 : 209.25 = 78.78 : x
2. Step 2: Convert to fraction form
   139.62/209.25 = 78.78/x
3. Step 3: Cross multiply
   139.62x = 209.25 × 78.78
4. Step 4: Simplify right side
   139.62x = 16,484.72
5. Step 5: Solve for x
   x = 16,484.72/139.62
6. Step 6: Final answer
   x = 118.07