Finding the Fourth Proportional to 85.42, 128.18 and 39.78

Step by Step Solution

1. Step 1: Write the proportion equation
   85.42 : 128.18 = 39.78 : x
2. Step 2: Convert to fraction form
   85.42/128.18 = 39.78/x
3. Step 3: Cross multiply
   85.42x = 128.18 × 39.78
4. Step 4: Simplify right side
   85.42x = 5,099.00
5. Step 5: Solve for x
   x = 5,099.00/85.42
6. Step 6: Final answer
   x = 59.69