Finding the Fourth Proportional to 128.17, 176.89 and 72.91

Step by Step Solution

1. Step 1: Write the proportion equation
   128.17 : 176.89 = 72.91 : x
2. Step 2: Convert to fraction form
   128.17/176.89 = 72.91/x
3. Step 3: Cross multiply
   128.17x = 176.89 × 72.91
4. Step 4: Simplify right side
   128.17x = 12,897.05
5. Step 5: Solve for x
   x = 12,897.05/128.17
6. Step 6: Final answer
   x = 100.62