Finding the Fourth Proportional to 85.79, 128.72 and 42.49

Step by Step Solution

1. Step 1: Write the proportion equation
   85.79 : 128.72 = 42.49 : x
2. Step 2: Convert to fraction form
   85.79/128.72 = 42.49/x
3. Step 3: Cross multiply
   85.79x = 128.72 × 42.49
4. Step 4: Simplify right side
   85.79x = 5,469.58
5. Step 5: Solve for x
   x = 5,469.58/85.79
6. Step 6: Final answer
   x = 63.75