Finding the Fourth Proportional to 85.59, 128.39 and 78.17

Step by Step Solution

1. Step 1: Write the proportion equation
   85.59 : 128.39 = 78.17 : x
2. Step 2: Convert to fraction form
   85.59/128.39 = 78.17/x
3. Step 3: Cross multiply
   85.59x = 128.39 × 78.17
4. Step 4: Simplify right side
   85.59x = 10,035.21
5. Step 5: Solve for x
   x = 10,035.21/85.59
6. Step 6: Final answer
   x = 117.25