Finding the Fourth Proportional to 86.13, 128.25 and 83.61

Step by Step Solution

1. Step 1: Write the proportion equation
   86.13 : 128.25 = 83.61 : x
2. Step 2: Convert to fraction form
   86.13/128.25 = 83.61/x
3. Step 3: Cross multiply
   86.13x = 128.25 × 83.61
4. Step 4: Simplify right side
   86.13x = 10,722.98
5. Step 5: Solve for x
   x = 10,722.98/86.13
6. Step 6: Final answer
   x = 124.50