Finding the Fourth Proportional to 85.46, 128.18 and 78.57

Step by Step Solution

1. Step 1: Write the proportion equation
   85.46 : 128.18 = 78.57 : x
2. Step 2: Convert to fraction form
   85.46/128.18 = 78.57/x
3. Step 3: Cross multiply
   85.46x = 128.18 × 78.57
4. Step 4: Simplify right side
   85.46x = 10,071.30
5. Step 5: Solve for x
   x = 10,071.30/85.46
6. Step 6: Final answer
   x = 117.86