Finding the Fourth Proportional to 139.72, 209.61 and 99.39

Step by Step Solution

1. Step 1: Write the proportion equation
   139.72 : 209.61 = 99.39 : x
2. Step 2: Convert to fraction form
   139.72/209.61 = 99.39/x
3. Step 3: Cross multiply
   139.72x = 209.61 × 99.39
4. Step 4: Simplify right side
   139.72x = 20,834.20
5. Step 5: Solve for x
   x = 20,834.20/139.72
6. Step 6: Final answer
   x = 149.12