Finding the Fourth Proportional to 85.49, 128.15 and 39.88

Step by Step Solution

1. Step 1: Write the proportion equation
   85.49 : 128.15 = 39.88 : x
2. Step 2: Convert to fraction form
   85.49/128.15 = 39.88/x
3. Step 3: Cross multiply
   85.49x = 128.15 × 39.88
4. Step 4: Simplify right side
   85.49x = 5,109.98
5. Step 5: Solve for x
   x = 5,109.98/85.49
6. Step 6: Final answer
   x = 59.77