Finding the Fourth Proportional to 128.76, 177.69 and 76.31

Step by Step Solution

1. Step 1: Write the proportion equation
   128.76 : 177.69 = 76.31 : x
2. Step 2: Convert to fraction form
   128.76/177.69 = 76.31/x
3. Step 3: Cross multiply
   128.76x = 177.69 × 76.31
4. Step 4: Simplify right side
   128.76x = 13,559.59
5. Step 5: Solve for x
   x = 13,559.59/128.76
6. Step 6: Final answer
   x = 105.31