Finding the Fourth Proportional to 105.78, 145.92 and 83.91

Step by Step Solution

1. Step 1: Write the proportion equation
   105.78 : 145.92 = 83.91 : x
2. Step 2: Convert to fraction form
   105.78/145.92 = 83.91/x
3. Step 3: Cross multiply
   105.78x = 145.92 × 83.91
4. Step 4: Simplify right side
   105.78x = 12,244.15
5. Step 5: Solve for x
   x = 12,244.15/105.78
6. Step 6: Final answer
   x = 115.75