Finding the Fourth Proportional to 100.71, 139.05 and 78.84

Step by Step Solution

1. Step 1: Write the proportion equation
   100.71 : 139.05 = 78.84 : x
2. Step 2: Convert to fraction form
   100.71/139.05 = 78.84/x
3. Step 3: Cross multiply
   100.71x = 139.05 × 78.84
4. Step 4: Simplify right side
   100.71x = 10,962.70
5. Step 5: Solve for x
   x = 10,962.70/100.71
6. Step 6: Final answer
   x = 108.85