Finding the Fourth Proportional to 85.78, 128.67 and 42.98

Step by Step Solution

1. Step 1: Write the proportion equation
   85.78 : 128.67 = 42.98 : x
2. Step 2: Convert to fraction form
   85.78/128.67 = 42.98/x
3. Step 3: Cross multiply
   85.78x = 128.67 × 42.98
4. Step 4: Simplify right side
   85.78x = 5,530.24
5. Step 5: Solve for x
   x = 5,530.24/85.78
6. Step 6: Final answer
   x = 64.47