Finding the Fourth Proportional to 21,057.76, 31,550.94 and 12,720.25

Step by Step Solution

1. Step 1: Write the proportion equation
   21,057.76 : 31,550.94 = 12,720.25 : x
2. Step 2: Convert to fraction form
   21,057.76/31,550.94 = 12,720.25/x
3. Step 3: Cross multiply
   21,057.76x = 31,550.94 × 12,720.25
4. Step 4: Simplify right side
   21,057.76x = 401,335,844.54
5. Step 5: Solve for x
   x = 401,335,844.54/21,057.76
6. Step 6: Final answer
   x = 19,058.81