Finding the Fourth Proportional to 86.16, 118.56 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   86.16 : 118.56 = 78.72 : x
2. Step 2: Convert to fraction form
   86.16/118.56 = 78.72/x
3. Step 3: Cross multiply
   86.16x = 118.56 × 78.72
4. Step 4: Simplify right side
   86.16x = 9,333.04
5. Step 5: Solve for x
   x = 9,333.04/86.16
6. Step 6: Final answer
   x = 108.32