Finding the Fourth Proportional to 128.98, 193.35 and 56.78

Step by Step Solution

1. Step 1: Write the proportion equation
   128.98 : 193.35 = 56.78 : x
2. Step 2: Convert to fraction form
   128.98/193.35 = 56.78/x
3. Step 3: Cross multiply
   128.98x = 193.35 × 56.78
4. Step 4: Simplify right side
   128.98x = 10,978.41
5. Step 5: Solve for x
   x = 10,978.41/128.98
6. Step 6: Final answer
   x = 85.12