Finding the Fourth Proportional to 1,389.63, 2,080.29 and 840.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.63 : 2,080.29 = 840.15 : x
2. Step 2: Convert to fraction form
   1,389.63/2,080.29 = 840.15/x
3. Step 3: Cross multiply
   1,389.63x = 2,080.29 × 840.15
4. Step 4: Simplify right side
   1,389.63x = 1,747,755.64
5. Step 5: Solve for x
   x = 1,747,755.64/1,389.63
6. Step 6: Final answer
   x = 1,257.71