Finding the Fourth Proportional to 139.98, 209.74 and 123.78

Step by Step Solution

1. Step 1: Write the proportion equation
   139.98 : 209.74 = 123.78 : x
2. Step 2: Convert to fraction form
   139.98/209.74 = 123.78/x
3. Step 3: Cross multiply
   139.98x = 209.74 × 123.78
4. Step 4: Simplify right side
   139.98x = 25,961.15
5. Step 5: Solve for x
   x = 25,961.15/139.98
6. Step 6: Final answer
   x = 185.47