Finding the Fourth Proportional to 105.72, 145.59 and 99.57

Step by Step Solution

1. Step 1: Write the proportion equation
   105.72 : 145.59 = 99.57 : x
2. Step 2: Convert to fraction form
   105.72/145.59 = 99.57/x
3. Step 3: Cross multiply
   105.72x = 145.59 × 99.57
4. Step 4: Simplify right side
   105.72x = 14,496.40
5. Step 5: Solve for x
   x = 14,496.40/105.72
6. Step 6: Final answer
   x = 137.12