Finding the Fourth Proportional to 85.69, 128.50 and 61.30

Step by Step Solution

1. Step 1: Write the proportion equation
   85.69 : 128.50 = 61.30 : x
2. Step 2: Convert to fraction form
   85.69/128.50 = 61.30/x
3. Step 3: Cross multiply
   85.69x = 128.50 × 61.30
4. Step 4: Simplify right side
   85.69x = 7,877.05
5. Step 5: Solve for x
   x = 7,877.05/85.69
6. Step 6: Final answer
   x = 91.92