Finding the Fourth Proportional to 21,839.20, 30,138.12 and 12,886.72

Step by Step Solution

1. Step 1: Write the proportion equation
   21,839.20 : 30,138.12 = 12,886.72 : x
2. Step 2: Convert to fraction form
   21,839.20/30,138.12 = 12,886.72/x
3. Step 3: Cross multiply
   21,839.20x = 30,138.12 × 12,886.72
4. Step 4: Simplify right side
   21,839.20x = 388,381,513.77
5. Step 5: Solve for x
   x = 388,381,513.77/21,839.20
6. Step 6: Final answer
   x = 17,783.69