Finding the Fourth Proportional to 78.78, 108.72 and 61.50

Step by Step Solution

1. Step 1: Write the proportion equation
   78.78 : 108.72 = 61.50 : x
2. Step 2: Convert to fraction form
   78.78/108.72 = 61.50/x
3. Step 3: Cross multiply
   78.78x = 108.72 × 61.50
4. Step 4: Simplify right side
   78.78x = 6,686.28
5. Step 5: Solve for x
   x = 6,686.28/78.78
6. Step 6: Final answer
   x = 84.87