Finding the Fourth Proportional to 111.72, 154.01 and 78.91

Step by Step Solution

1. Step 1: Write the proportion equation
   111.72 : 154.01 = 78.91 : x
2. Step 2: Convert to fraction form
   111.72/154.01 = 78.91/x
3. Step 3: Cross multiply
   111.72x = 154.01 × 78.91
4. Step 4: Simplify right side
   111.72x = 12,152.93
5. Step 5: Solve for x
   x = 12,152.93/111.72
6. Step 6: Final answer
   x = 108.78