Finding the Fourth Proportional to 139.71, 208.71 and 90.56

Step by Step Solution

1. Step 1: Write the proportion equation
   139.71 : 208.71 = 90.56 : x
2. Step 2: Convert to fraction form
   139.71/208.71 = 90.56/x
3. Step 3: Cross multiply
   139.71x = 208.71 × 90.56
4. Step 4: Simplify right side
   139.71x = 18,899.73
5. Step 5: Solve for x
   x = 18,899.73/139.71
6. Step 6: Final answer
   x = 135.28