Finding the Fourth Proportional to 85.56, 128.28 and 42.21

Step by Step Solution

1. Step 1: Write the proportion equation
   85.56 : 128.28 = 42.21 : x
2. Step 2: Convert to fraction form
   85.56/128.28 = 42.21/x
3. Step 3: Cross multiply
   85.56x = 128.28 × 42.21
4. Step 4: Simplify right side
   85.56x = 5,414.70
5. Step 5: Solve for x
   x = 5,414.70/85.56
6. Step 6: Final answer
   x = 63.29