Finding the Fourth Proportional to 1,139.58, 1,572.48 and 642.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.58 : 1,572.48 = 642.15 : x
2. Step 2: Convert to fraction form
   1,139.58/1,572.48 = 642.15/x
3. Step 3: Cross multiply
   1,139.58x = 1,572.48 × 642.15
4. Step 4: Simplify right side
   1,139.58x = 1,009,768.03
5. Step 5: Solve for x
   x = 1,009,768.03/1,139.58
6. Step 6: Final answer
   x = 886.09