Finding the Fourth Proportional to 85.42, 128.06 and 31.31

Step by Step Solution

1. Step 1: Write the proportion equation
   85.42 : 128.06 = 31.31 : x
2. Step 2: Convert to fraction form
   85.42/128.06 = 31.31/x
3. Step 3: Cross multiply
   85.42x = 128.06 × 31.31
4. Step 4: Simplify right side
   85.42x = 4,009.15
5. Step 5: Solve for x
   x = 4,009.15/85.42
6. Step 6: Final answer
   x = 46.93