Finding the Fourth Proportional to 86.31, 128.77 and 78.46

Step by Step Solution

1. Step 1: Write the proportion equation
   86.31 : 128.77 = 78.46 : x
2. Step 2: Convert to fraction form
   86.31/128.77 = 78.46/x
3. Step 3: Cross multiply
   86.31x = 128.77 × 78.46
4. Step 4: Simplify right side
   86.31x = 10,102.78
5. Step 5: Solve for x
   x = 10,102.78/86.31
6. Step 6: Final answer
   x = 117.05