Finding the Fourth Proportional to 128.72, 192.72 and 109.40

Step by Step Solution

1. Step 1: Write the proportion equation
   128.72 : 192.72 = 109.40 : x
2. Step 2: Convert to fraction form
   128.72/192.72 = 109.40/x
3. Step 3: Cross multiply
   128.72x = 192.72 × 109.40
4. Step 4: Simplify right side
   128.72x = 21,083.57
5. Step 5: Solve for x
   x = 21,083.57/128.72
6. Step 6: Final answer
   x = 163.79