Finding the Fourth Proportional to 100.92, 139.30 and 78.78

Step by Step Solution

1. Step 1: Write the proportion equation
   100.92 : 139.30 = 78.78 : x
2. Step 2: Convert to fraction form
   100.92/139.30 = 78.78/x
3. Step 3: Cross multiply
   100.92x = 139.30 × 78.78
4. Step 4: Simplify right side
   100.92x = 10,974.05
5. Step 5: Solve for x
   x = 10,974.05/100.92
6. Step 6: Final answer
   x = 108.74