Finding the Fourth Proportional to 120.18, 165.78 and 78.72

Step by Step Solution

1. Step 1: Write the proportion equation
   120.18 : 165.78 = 78.72 : x
2. Step 2: Convert to fraction form
   120.18/165.78 = 78.72/x
3. Step 3: Cross multiply
   120.18x = 165.78 × 78.72
4. Step 4: Simplify right side
   120.18x = 13,050.20
5. Step 5: Solve for x
   x = 13,050.20/120.18
6. Step 6: Final answer
   x = 108.59