Finding the Fourth Proportional to 139.28, 208.42 and 90.50

Step by Step Solution

1. Step 1: Write the proportion equation
   139.28 : 208.42 = 90.50 : x
2. Step 2: Convert to fraction form
   139.28/208.42 = 90.50/x
3. Step 3: Cross multiply
   139.28x = 208.42 × 90.50
4. Step 4: Simplify right side
   139.28x = 18,860.74
5. Step 5: Solve for x
   x = 18,860.74/139.28
6. Step 6: Final answer
   x = 135.42