Finding the Fourth Proportional to 100.78, 139.08 and 76.17

Step by Step Solution

1. Step 1: Write the proportion equation
   100.78 : 139.08 = 76.17 : x
2. Step 2: Convert to fraction form
   100.78/139.08 = 76.17/x
3. Step 3: Cross multiply
   100.78x = 139.08 × 76.17
4. Step 4: Simplify right side
   100.78x = 10,593.34
5. Step 5: Solve for x
   x = 10,593.34/100.78
6. Step 6: Final answer
   x = 105.12