Finding the Fourth Proportional to 128.56, 192.89 and 105.78

Step by Step Solution

1. Step 1: Write the proportion equation
   128.56 : 192.89 = 105.78 : x
2. Step 2: Convert to fraction form
   128.56/192.89 = 105.78/x
3. Step 3: Cross multiply
   128.56x = 192.89 × 105.78
4. Step 4: Simplify right side
   128.56x = 20,403.90
5. Step 5: Solve for x
   x = 20,403.90/128.56
6. Step 6: Final answer
   x = 158.71