Finding the Fourth Proportional to 85.43, 128.07 and 42.09

Step by Step Solution

1. Step 1: Write the proportion equation
   85.43 : 128.07 = 42.09 : x
2. Step 2: Convert to fraction form
   85.43/128.07 = 42.09/x
3. Step 3: Cross multiply
   85.43x = 128.07 × 42.09
4. Step 4: Simplify right side
   85.43x = 5,390.47
5. Step 5: Solve for x
   x = 5,390.47/85.43
6. Step 6: Final answer
   x = 63.10