Finding the Fourth Proportional to 1,081.20, 1,491.98 and 639.08

Step by Step Solution

1. Step 1: Write the proportion equation
   1,081.20 : 1,491.98 = 639.08 : x
2. Step 2: Convert to fraction form
   1,081.20/1,491.98 = 639.08/x
3. Step 3: Cross multiply
   1,081.20x = 1,491.98 × 639.08
4. Step 4: Simplify right side
   1,081.20x = 953,494.58
5. Step 5: Solve for x
   x = 953,494.58/1,081.20
6. Step 6: Final answer
   x = 881.89