Finding the Fourth Proportional to 100.28, 138.48 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   100.28 : 138.48 = 78.72 : x
2. Step 2: Convert to fraction form
   100.28/138.48 = 78.72/x
3. Step 3: Cross multiply
   100.28x = 138.48 × 78.72
4. Step 4: Simplify right side
   100.28x = 10,901.15
5. Step 5: Solve for x
   x = 10,901.15/100.28
6. Step 6: Final answer
   x = 108.71