Finding the Fourth Proportional to 89.72, 133.69 and 86.28

Step by Step Solution

1. Step 1: Write the proportion equation
   89.72 : 133.69 = 86.28 : x
2. Step 2: Convert to fraction form
   89.72/133.69 = 86.28/x
3. Step 3: Cross multiply
   89.72x = 133.69 × 86.28
4. Step 4: Simplify right side
   89.72x = 11,534.77
5. Step 5: Solve for x
   x = 11,534.77/89.72
6. Step 6: Final answer
   x = 128.56