Finding the Fourth Proportional to 85.86, 128.84 and 78.30

Step by Step Solution

1. Step 1: Write the proportion equation
   85.86 : 128.84 = 78.30 : x
2. Step 2: Convert to fraction form
   85.86/128.84 = 78.30/x
3. Step 3: Cross multiply
   85.86x = 128.84 × 78.30
4. Step 4: Simplify right side
   85.86x = 10,087.78
5. Step 5: Solve for x
   x = 10,087.78/85.86
6. Step 6: Final answer
   x = 117.49