Finding the Fourth Proportional to 85.81, 128.61 and 42.50

Step by Step Solution

1. Step 1: Write the proportion equation
   85.81 : 128.61 = 42.50 : x
2. Step 2: Convert to fraction form
   85.81/128.61 = 42.50/x
3. Step 3: Cross multiply
   85.81x = 128.61 × 42.50
4. Step 4: Simplify right side
   85.81x = 5,466.28
5. Step 5: Solve for x
   x = 5,466.28/85.81
6. Step 6: Final answer
   x = 63.70