Finding the Fourth Proportional to 100.87, 139.25 and 90.61

Step by Step Solution

1. Step 1: Write the proportion equation
   100.87 : 139.25 = 90.61 : x
2. Step 2: Convert to fraction form
   100.87/139.25 = 90.61/x
3. Step 3: Cross multiply
   100.87x = 139.25 × 90.61
4. Step 4: Simplify right side
   100.87x = 12,617.32
5. Step 5: Solve for x
   x = 12,617.32/100.87
6. Step 6: Final answer
   x = 125.09