Finding the Fourth Proportional to 139.42, 208.79 and 81.52

Step by Step Solution

1. Step 1: Write the proportion equation
   139.42 : 208.79 = 81.52 : x
2. Step 2: Convert to fraction form
   139.42/208.79 = 81.52/x
3. Step 3: Cross multiply
   139.42x = 208.79 × 81.52
4. Step 4: Simplify right side
   139.42x = 17,019.52
5. Step 5: Solve for x
   x = 17,019.52/139.42
6. Step 6: Final answer
   x = 122.07