Finding the Fourth Proportional to 1,080.78, 1,491.75 and 639.06

Step by Step Solution

1. Step 1: Write the proportion equation
   1,080.78 : 1,491.75 = 639.06 : x
2. Step 2: Convert to fraction form
   1,080.78/1,491.75 = 639.06/x
3. Step 3: Cross multiply
   1,080.78x = 1,491.75 × 639.06
4. Step 4: Simplify right side
   1,080.78x = 953,317.76
5. Step 5: Solve for x
   x = 953,317.76/1,080.78
6. Step 6: Final answer
   x = 882.06