Finding the Fourth Proportional to 1,139.30, 1,572.28 and 642

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.30 : 1,572.28 = 642 : x
2. Step 2: Convert to fraction form
   1,139.30/1,572.28 = 642/x
3. Step 3: Cross multiply
   1,139.30x = 1,572.28 × 642
4. Step 4: Simplify right side
   1,139.30x = 1,009,403.76
5. Step 5: Solve for x
   x = 1,009,403.76/1,139.30
6. Step 6: Final answer
   x = 885.99