Finding the Fourth Proportional to 105.18, 145.18 and 72.40

Step by Step Solution

1. Step 1: Write the proportion equation
   105.18 : 145.18 = 72.40 : x
2. Step 2: Convert to fraction form
   105.18/145.18 = 72.40/x
3. Step 3: Cross multiply
   105.18x = 145.18 × 72.40
4. Step 4: Simplify right side
   105.18x = 10,511.03
5. Step 5: Solve for x
   x = 10,511.03/105.18
6. Step 6: Final answer
   x = 99.93