Finding the Fourth Proportional to 128.59, 177.42 and 78.79

Step by Step Solution

1. Step 1: Write the proportion equation
   128.59 : 177.42 = 78.79 : x
2. Step 2: Convert to fraction form
   128.59/177.42 = 78.79/x
3. Step 3: Cross multiply
   128.59x = 177.42 × 78.79
4. Step 4: Simplify right side
   128.59x = 13,978.92
5. Step 5: Solve for x
   x = 13,978.92/128.59
6. Step 6: Final answer
   x = 108.71