Finding the Fourth Proportional to 1,139.43, 1,572.31 and 642.02

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.43 : 1,572.31 = 642.02 : x
2. Step 2: Convert to fraction form
   1,139.43/1,572.31 = 642.02/x
3. Step 3: Cross multiply
   1,139.43x = 1,572.31 × 642.02
4. Step 4: Simplify right side
   1,139.43x = 1,009,451.26
5. Step 5: Solve for x
   x = 1,009,451.26/1,139.43
6. Step 6: Final answer
   x = 885.93