Finding the Fourth Proportional to 1,139.49, 1,572.42 and 642.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.49 : 1,572.42 = 642.15 : x
2. Step 2: Convert to fraction form
   1,139.49/1,572.42 = 642.15/x
3. Step 3: Cross multiply
   1,139.49x = 1,572.42 × 642.15
4. Step 4: Simplify right side
   1,139.49x = 1,009,729.50
5. Step 5: Solve for x
   x = 1,009,729.50/1,139.49
6. Step 6: Final answer
   x = 886.12