Finding the Fourth Proportional to 86.16, 128.60 and 78.12

Step by Step Solution

1. Step 1: Write the proportion equation
   86.16 : 128.60 = 78.12 : x
2. Step 2: Convert to fraction form
   86.16/128.60 = 78.12/x
3. Step 3: Cross multiply
   86.16x = 128.60 × 78.12
4. Step 4: Simplify right side
   86.16x = 10,046.23
5. Step 5: Solve for x
   x = 10,046.23/86.16
6. Step 6: Final answer
   x = 116.60