Finding the Fourth Proportional to 105.78, 158.54 and 81.33

Step by Step Solution

1. Step 1: Write the proportion equation
   105.78 : 158.54 = 81.33 : x
2. Step 2: Convert to fraction form
   105.78/158.54 = 81.33/x
3. Step 3: Cross multiply
   105.78x = 158.54 × 81.33
4. Step 4: Simplify right side
   105.78x = 12,892.86
5. Step 5: Solve for x
   x = 12,892.86/105.78
6. Step 6: Final answer
   x = 121.89