Finding the Fourth Proportional to 1,139.25, 1,572.15 and 642.05

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.25 : 1,572.15 = 642.05 : x
2. Step 2: Convert to fraction form
   1,139.25/1,572.15 = 642.05/x
3. Step 3: Cross multiply
   1,139.25x = 1,572.15 × 642.05
4. Step 4: Simplify right side
   1,139.25x = 1,009,396.58
5. Step 5: Solve for x
   x = 1,009,396.58/1,139.25
6. Step 6: Final answer
   x = 886.02