Finding the Fourth Proportional to 85.42, 117.89 and 78.81

Step by Step Solution

1. Step 1: Write the proportion equation
   85.42 : 117.89 = 78.81 : x
2. Step 2: Convert to fraction form
   85.42/117.89 = 78.81/x
3. Step 3: Cross multiply
   85.42x = 117.89 × 78.81
4. Step 4: Simplify right side
   85.42x = 9,290.91
5. Step 5: Solve for x
   x = 9,290.91/85.42
6. Step 6: Final answer
   x = 108.77