Finding the Fourth Proportional to 139.69, 209.47 and 42.15

Step by Step Solution

1. Step 1: Write the proportion equation
   139.69 : 209.47 = 42.15 : x
2. Step 2: Convert to fraction form
   139.69/209.47 = 42.15/x
3. Step 3: Cross multiply
   139.69x = 209.47 × 42.15
4. Step 4: Simplify right side
   139.69x = 8,828.58
5. Step 5: Solve for x
   x = 8,828.58/139.69
6. Step 6: Final answer
   x = 63.20