Finding the Fourth Proportional to 111.40, 153.68 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   111.40 : 153.68 = 78.72 : x
2. Step 2: Convert to fraction form
   111.40/153.68 = 78.72/x
3. Step 3: Cross multiply
   111.40x = 153.68 × 78.72
4. Step 4: Simplify right side
   111.40x = 12,097.69
5. Step 5: Solve for x
   x = 12,097.69/111.40
6. Step 6: Final answer
   x = 108.60