Finding the Fourth Proportional to 78.58, 108.18 and 64.78

Step by Step Solution

1. Step 1: Write the proportion equation
   78.58 : 108.18 = 64.78 : x
2. Step 2: Convert to fraction form
   78.58/108.18 = 64.78/x
3. Step 3: Cross multiply
   78.58x = 108.18 × 64.78
4. Step 4: Simplify right side
   78.58x = 7,007.90
5. Step 5: Solve for x
   x = 7,007.90/78.58
6. Step 6: Final answer
   x = 89.18