Finding the Fourth Proportional to 105.31, 145.20 and 85.57

Step by Step Solution

1. Step 1: Write the proportion equation
   105.31 : 145.20 = 85.57 : x
2. Step 2: Convert to fraction form
   105.31/145.20 = 85.57/x
3. Step 3: Cross multiply
   105.31x = 145.20 × 85.57
4. Step 4: Simplify right side
   105.31x = 12,425.30
5. Step 5: Solve for x
   x = 12,425.30/105.31
6. Step 6: Final answer
   x = 117.99