Finding the Fourth Proportional to 128.72, 177.53 and 89.31

Step by Step Solution

1. Step 1: Write the proportion equation
   128.72 : 177.53 = 89.31 : x
2. Step 2: Convert to fraction form
   128.72/177.53 = 89.31/x
3. Step 3: Cross multiply
   128.72x = 177.53 × 89.31
4. Step 4: Simplify right side
   128.72x = 15,854.76
5. Step 5: Solve for x
   x = 15,854.76/128.72
6. Step 6: Final answer
   x = 123.18