Finding the Fourth Proportional to 85.77, 128.64 and 42.42

Step by Step Solution

1. Step 1: Write the proportion equation
   85.77 : 128.64 = 42.42 : x
2. Step 2: Convert to fraction form
   85.77/128.64 = 42.42/x
3. Step 3: Cross multiply
   85.77x = 128.64 × 42.42
4. Step 4: Simplify right side
   85.77x = 5,456.91
5. Step 5: Solve for x
   x = 5,456.91/85.77
6. Step 6: Final answer
   x = 63.62