Finding the Fourth Proportional to 85.56, 128.87 and 78.16

Step by Step Solution

1. Step 1: Write the proportion equation
   85.56 : 128.87 = 78.16 : x
2. Step 2: Convert to fraction form
   85.56/128.87 = 78.16/x
3. Step 3: Cross multiply
   85.56x = 128.87 × 78.16
4. Step 4: Simplify right side
   85.56x = 10,072.48
5. Step 5: Solve for x
   x = 10,072.48/85.56
6. Step 6: Final answer
   x = 117.72