Finding the Fourth Proportional to 85.91, 128.89 and 42.58

Step by Step Solution

1. Step 1: Write the proportion equation
   85.91 : 128.89 = 42.58 : x
2. Step 2: Convert to fraction form
   85.91/128.89 = 42.58/x
3. Step 3: Cross multiply
   85.91x = 128.89 × 42.58
4. Step 4: Simplify right side
   85.91x = 5,488.14
5. Step 5: Solve for x
   x = 5,488.14/85.91
6. Step 6: Final answer
   x = 63.88