Finding the Fourth Proportional to 139.78, 192.85 and 90.72

Step by Step Solution

1. Step 1: Write the proportion equation
   139.78 : 192.85 = 90.72 : x
2. Step 2: Convert to fraction form
   139.78/192.85 = 90.72/x
3. Step 3: Cross multiply
   139.78x = 192.85 × 90.72
4. Step 4: Simplify right side
   139.78x = 17,495.35
5. Step 5: Solve for x
   x = 17,495.35/139.78
6. Step 6: Final answer
   x = 125.16