Finding the Fourth Proportional to 121.72, 168.02 and 78.05

Step by Step Solution

1. Step 1: Write the proportion equation
   121.72 : 168.02 = 78.05 : x
2. Step 2: Convert to fraction form
   121.72/168.02 = 78.05/x
3. Step 3: Cross multiply
   121.72x = 168.02 × 78.05
4. Step 4: Simplify right side
   121.72x = 13,113.32
5. Step 5: Solve for x
   x = 13,113.32/121.72
6. Step 6: Final answer
   x = 107.74