Finding the Fourth Proportional to 85.40, 128.00 and 42.09

Step by Step Solution

1. Step 1: Write the proportion equation
   85.40 : 128.00 = 42.09 : x
2. Step 2: Convert to fraction form
   85.40/128.00 = 42.09/x
3. Step 3: Cross multiply
   85.40x = 128.00 × 42.09
4. Step 4: Simplify right side
   85.40x = 5,387.31
5. Step 5: Solve for x
   x = 5,387.31/85.40
6. Step 6: Final answer
   x = 63.09