Finding the Fourth Proportional to 105.72, 145.98 and 78.12

Step by Step Solution

1. Step 1: Write the proportion equation
   105.72 : 145.98 = 78.12 : x
2. Step 2: Convert to fraction form
   105.72/145.98 = 78.12/x
3. Step 3: Cross multiply
   105.72x = 145.98 × 78.12
4. Step 4: Simplify right side
   105.72x = 11,403.96
5. Step 5: Solve for x
   x = 11,403.96/105.72
6. Step 6: Final answer
   x = 107.87