Finding the Fourth Proportional to 85.78, 118.42 and 64.10

Step by Step Solution

1. Step 1: Write the proportion equation
   85.78 : 118.42 = 64.10 : x
2. Step 2: Convert to fraction form
   85.78/118.42 = 64.10/x
3. Step 3: Cross multiply
   85.78x = 118.42 × 64.10
4. Step 4: Simplify right side
   85.78x = 7,590.72
5. Step 5: Solve for x
   x = 7,590.72/85.78
6. Step 6: Final answer
   x = 88.49