Finding the Fourth Proportional to 86.36, 128.69 and 83.75

Step by Step Solution

1. Step 1: Write the proportion equation
   86.36 : 128.69 = 83.75 : x
2. Step 2: Convert to fraction form
   86.36/128.69 = 83.75/x
3. Step 3: Cross multiply
   86.36x = 128.69 × 83.75
4. Step 4: Simplify right side
   86.36x = 10,778.32
5. Step 5: Solve for x
   x = 10,778.32/86.36
6. Step 6: Final answer
   x = 124.81