Finding the Fourth Proportional to 21,478.02, 29,640 and 12,978.96

Step by Step Solution

1. Step 1: Write the proportion equation
   21,478.02 : 29,640 = 12,978.96 : x
2. Step 2: Convert to fraction form
   21,478.02/29,640 = 12,978.96/x
3. Step 3: Cross multiply
   21,478.02x = 29,640 × 12,978.96
4. Step 4: Simplify right side
   21,478.02x = 384,696,374.40
5. Step 5: Solve for x
   x = 384,696,374.40/21,478.02
6. Step 6: Final answer
   x = 17,911.17