Finding the Fourth Proportional to 78.61, 107.55 and 78.31

Step by Step Solution

1. Step 1: Write the proportion equation
   78.61 : 107.55 = 78.31 : x
2. Step 2: Convert to fraction form
   78.61/107.55 = 78.31/x
3. Step 3: Cross multiply
   78.61x = 107.55 × 78.31
4. Step 4: Simplify right side
   78.61x = 8,421.31
5. Step 5: Solve for x
   x = 8,421.31/78.61
6. Step 6: Final answer
   x = 107.13