Finding the Fourth Proportional to 139.05, 191.86 and 83.78

Step by Step Solution

1. Step 1: Write the proportion equation
   139.05 : 191.86 = 83.78 : x
2. Step 2: Convert to fraction form
   139.05/191.86 = 83.78/x
3. Step 3: Cross multiply
   139.05x = 191.86 × 83.78
4. Step 4: Simplify right side
   139.05x = 16,074.03
5. Step 5: Solve for x
   x = 16,074.03/139.05
6. Step 6: Final answer
   x = 115.60