Finding the Fourth Proportional to 100.94, 139.20 and 78.81

Step by Step Solution

1. Step 1: Write the proportion equation
   100.94 : 139.20 = 78.81 : x
2. Step 2: Convert to fraction form
   100.94/139.20 = 78.81/x
3. Step 3: Cross multiply
   100.94x = 139.20 × 78.81
4. Step 4: Simplify right side
   100.94x = 10,970.35
5. Step 5: Solve for x
   x = 10,970.35/100.94
6. Step 6: Final answer
   x = 108.69