Finding the Fourth Proportional to 111.71, 154.15 and 78.91

Step by Step Solution

1. Step 1: Write the proportion equation
   111.71 : 154.15 = 78.91 : x
2. Step 2: Convert to fraction form
   111.71/154.15 = 78.91/x
3. Step 3: Cross multiply
   111.71x = 154.15 × 78.91
4. Step 4: Simplify right side
   111.71x = 12,163.98
5. Step 5: Solve for x
   x = 12,163.98/111.71
6. Step 6: Final answer
   x = 108.89