Finding the Fourth Proportional to 105.71, 158.31 and 78.21

Step by Step Solution

1. Step 1: Write the proportion equation
   105.71 : 158.31 = 78.21 : x
2. Step 2: Convert to fraction form
   105.71/158.31 = 78.21/x
3. Step 3: Cross multiply
   105.71x = 158.31 × 78.21
4. Step 4: Simplify right side
   105.71x = 12,381.43
5. Step 5: Solve for x
   x = 12,381.43/105.71
6. Step 6: Final answer
   x = 117.13