Finding the Fourth Proportional to 128.05, 176.72 and 78.91

Step by Step Solution

1. Step 1: Write the proportion equation
   128.05 : 176.72 = 78.91 : x
2. Step 2: Convert to fraction form
   128.05/176.72 = 78.91/x
3. Step 3: Cross multiply
   128.05x = 176.72 × 78.91
4. Step 4: Simplify right side
   128.05x = 13,944.14
5. Step 5: Solve for x
   x = 13,944.14/128.05
6. Step 6: Final answer
   x = 108.90