Finding the Fourth Proportional to 139.79, 209.75 and 105.31

Step by Step Solution

1. Step 1: Write the proportion equation
   139.79 : 209.75 = 105.31 : x
2. Step 2: Convert to fraction form
   139.79/209.75 = 105.31/x
3. Step 3: Cross multiply
   139.79x = 209.75 × 105.31
4. Step 4: Simplify right side
   139.79x = 22,089.10
5. Step 5: Solve for x
   x = 22,089.10/139.79
6. Step 6: Final answer
   x = 158.02