Finding the Fourth Proportional to 85.28, 128.60 and 78.56

Step by Step Solution

1. Step 1: Write the proportion equation
   85.28 : 128.60 = 78.56 : x
2. Step 2: Convert to fraction form
   85.28/128.60 = 78.56/x
3. Step 3: Cross multiply
   85.28x = 128.60 × 78.56
4. Step 4: Simplify right side
   85.28x = 10,102.82
5. Step 5: Solve for x
   x = 10,102.82/85.28
6. Step 6: Final answer
   x = 118.47