Finding the Fourth Proportional to 139.79, 192.89 and 80.78

Step by Step Solution

1. Step 1: Write the proportion equation
   139.79 : 192.89 = 80.78 : x
2. Step 2: Convert to fraction form
   139.79/192.89 = 80.78/x
3. Step 3: Cross multiply
   139.79x = 192.89 × 80.78
4. Step 4: Simplify right side
   139.79x = 15,580.89
5. Step 5: Solve for x
   x = 15,580.89/139.79
6. Step 6: Final answer
   x = 111.46