Finding the Fourth Proportional to 21,979.51, 30,330.52 and 12,420.50

Step by Step Solution

1. Step 1: Write the proportion equation
   21,979.51 : 30,330.52 = 12,420.50 : x
2. Step 2: Convert to fraction form
   21,979.51/30,330.52 = 12,420.50/x
3. Step 3: Cross multiply
   21,979.51x = 30,330.52 × 12,420.50
4. Step 4: Simplify right side
   21,979.51x = 376,720,040.96
5. Step 5: Solve for x
   x = 376,720,040.96/21,979.51
6. Step 6: Final answer
   x = 17,139.60