Finding the Fourth Proportional to 128.72, 193.12 and 56.57

Step by Step Solution

1. Step 1: Write the proportion equation
   128.72 : 193.12 = 56.57 : x
2. Step 2: Convert to fraction form
   128.72/193.12 = 56.57/x
3. Step 3: Cross multiply
   128.72x = 193.12 × 56.57
4. Step 4: Simplify right side
   128.72x = 10,923.69
5. Step 5: Solve for x
   x = 10,923.69/128.72
6. Step 6: Final answer
   x = 84.86