Finding the Fourth Proportional to 78.69, 108.75 and 64.85

Step by Step Solution

1. Step 1: Write the proportion equation
   78.69 : 108.75 = 64.85 : x
2. Step 2: Convert to fraction form
   78.69/108.75 = 64.85/x
3. Step 3: Cross multiply
   78.69x = 108.75 × 64.85
4. Step 4: Simplify right side
   78.69x = 7,051.89
5. Step 5: Solve for x
   x = 7,051.89/78.69
6. Step 6: Final answer
   x = 89.62