Finding the Fourth Proportional to 128.50, 177.28 and 78.71

Step by Step Solution

1. Step 1: Write the proportion equation
   128.50 : 177.28 = 78.71 : x
2. Step 2: Convert to fraction form
   128.50/177.28 = 78.71/x
3. Step 3: Cross multiply
   128.50x = 177.28 × 78.71
4. Step 4: Simplify right side
   128.50x = 13,953.71
5. Step 5: Solve for x
   x = 13,953.71/128.50
6. Step 6: Final answer
   x = 108.59