Finding the Fourth Proportional to 139.72, 209.32 and 78.77

Step by Step Solution

1. Step 1: Write the proportion equation
   139.72 : 209.32 = 78.77 : x
2. Step 2: Convert to fraction form
   139.72/209.32 = 78.77/x
3. Step 3: Cross multiply
   139.72x = 209.32 × 78.77
4. Step 4: Simplify right side
   139.72x = 16,488.14
5. Step 5: Solve for x
   x = 16,488.14/139.72
6. Step 6: Final answer
   x = 118.01