Finding the Fourth Proportional to 139.61, 209.18 and 85.48

Step by Step Solution

1. Step 1: Write the proportion equation
   139.61 : 209.18 = 85.48 : x
2. Step 2: Convert to fraction form
   139.61/209.18 = 85.48/x
3. Step 3: Cross multiply
   139.61x = 209.18 × 85.48
4. Step 4: Simplify right side
   139.61x = 17,880.71
5. Step 5: Solve for x
   x = 17,880.71/139.61
6. Step 6: Final answer
   x = 128.08