Finding the Fourth Proportional to 111.72, 167.55 and 81.30

Step by Step Solution

1. Step 1: Write the proportion equation
   111.72 : 167.55 = 81.30 : x
2. Step 2: Convert to fraction form
   111.72/167.55 = 81.30/x
3. Step 3: Cross multiply
   111.72x = 167.55 × 81.30
4. Step 4: Simplify right side
   111.72x = 13,621.82
5. Step 5: Solve for x
   x = 13,621.82/111.72
6. Step 6: Final answer
   x = 121.93