Finding the Fourth Proportional to 139.86, 209.39 and 78.84

Step by Step Solution

1. Step 1: Write the proportion equation
   139.86 : 209.39 = 78.84 : x
2. Step 2: Convert to fraction form
   139.86/209.39 = 78.84/x
3. Step 3: Cross multiply
   139.86x = 209.39 × 78.84
4. Step 4: Simplify right side
   139.86x = 16,507.91
5. Step 5: Solve for x
   x = 16,507.91/139.86
6. Step 6: Final answer
   x = 118.03