Finding the Fourth Proportional to 86.10, 128.49 and 78.44

Step by Step Solution

1. Step 1: Write the proportion equation
   86.10 : 128.49 = 78.44 : x
2. Step 2: Convert to fraction form
   86.10/128.49 = 78.44/x
3. Step 3: Cross multiply
   86.10x = 128.49 × 78.44
4. Step 4: Simplify right side
   86.10x = 10,077.72
5. Step 5: Solve for x
   x = 10,077.72/86.10
6. Step 6: Final answer
   x = 117.05