Finding the Fourth Proportional to 105.31, 157.98 and 85.15

Step by Step Solution

1. Step 1: Write the proportion equation
   105.31 : 157.98 = 85.15 : x
2. Step 2: Convert to fraction form
   105.31/157.98 = 85.15/x
3. Step 3: Cross multiply
   105.31x = 157.98 × 85.15
4. Step 4: Simplify right side
   105.31x = 13,450.78
5. Step 5: Solve for x
   x = 13,450.78/105.31
6. Step 6: Final answer
   x = 127.73