Finding the Fourth Proportional to 1,139.59, 1,572.32 and 642.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.59 : 1,572.32 = 642.20 : x
2. Step 2: Convert to fraction form
   1,139.59/1,572.32 = 642.20/x
3. Step 3: Cross multiply
   1,139.59x = 1,572.32 × 642.20
4. Step 4: Simplify right side
   1,139.59x = 1,009,743.90
5. Step 5: Solve for x
   x = 1,009,743.90/1,139.59
6. Step 6: Final answer
   x = 886.06