Finding the Fourth Proportional to 85.50, 128.31 and 42.75

Step by Step Solution

1. Step 1: Write the proportion equation
   85.50 : 128.31 = 42.75 : x
2. Step 2: Convert to fraction form
   85.50/128.31 = 42.75/x
3. Step 3: Cross multiply
   85.50x = 128.31 × 42.75
4. Step 4: Simplify right side
   85.50x = 5,485.25
5. Step 5: Solve for x
   x = 5,485.25/85.50
6. Step 6: Final answer
   x = 64.16