Finding the Fourth Proportional to 111.72, 167.31 and 81.15

Step by Step Solution

1. Step 1: Write the proportion equation
   111.72 : 167.31 = 81.15 : x
2. Step 2: Convert to fraction form
   111.72/167.31 = 81.15/x
3. Step 3: Cross multiply
   111.72x = 167.31 × 81.15
4. Step 4: Simplify right side
   111.72x = 13,577.21
5. Step 5: Solve for x
   x = 13,577.21/111.72
6. Step 6: Final answer
   x = 121.53