Finding the Fourth Proportional to 105.18, 158.59 and 91.81

Step by Step Solution

1. Step 1: Write the proportion equation
   105.18 : 158.59 = 91.81 : x
2. Step 2: Convert to fraction form
   105.18/158.59 = 91.81/x
3. Step 3: Cross multiply
   105.18x = 158.59 × 91.81
4. Step 4: Simplify right side
   105.18x = 14,560.15
5. Step 5: Solve for x
   x = 14,560.15/105.18
6. Step 6: Final answer
   x = 138.43