Finding the Fourth Proportional to 86.35, 128.86 and 78.69

Step by Step Solution

1. Step 1: Write the proportion equation
   86.35 : 128.86 = 78.69 : x
2. Step 2: Convert to fraction form
   86.35/128.86 = 78.69/x
3. Step 3: Cross multiply
   86.35x = 128.86 × 78.69
4. Step 4: Simplify right side
   86.35x = 10,138.96
5. Step 5: Solve for x
   x = 10,138.96/86.35
6. Step 6: Final answer
   x = 117.42