Finding the Fourth Proportional to 139.56, 209.49 and 78.76

Step by Step Solution

1. Step 1: Write the proportion equation
   139.56 : 209.49 = 78.76 : x
2. Step 2: Convert to fraction form
   139.56/209.49 = 78.76/x
3. Step 3: Cross multiply
   139.56x = 209.49 × 78.76
4. Step 4: Simplify right side
   139.56x = 16,499.43
5. Step 5: Solve for x
   x = 16,499.43/139.56
6. Step 6: Final answer
   x = 118.23