Finding the Fourth Proportional to 139.20, 192.15 and 90.15

Step by Step Solution

1. Step 1: Write the proportion equation
   139.20 : 192.15 = 90.15 : x
2. Step 2: Convert to fraction form
   139.20/192.15 = 90.15/x
3. Step 3: Cross multiply
   139.20x = 192.15 × 90.15
4. Step 4: Simplify right side
   139.20x = 17,322.32
5. Step 5: Solve for x
   x = 17,322.32/139.20
6. Step 6: Final answer
   x = 124.44