Finding the Fourth Proportional to 1,139.22, 1,572.28 and 642.06

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.22 : 1,572.28 = 642.06 : x
2. Step 2: Convert to fraction form
   1,139.22/1,572.28 = 642.06/x
3. Step 3: Cross multiply
   1,139.22x = 1,572.28 × 642.06
4. Step 4: Simplify right side
   1,139.22x = 1,009,498.10
5. Step 5: Solve for x
   x = 1,009,498.10/1,139.22
6. Step 6: Final answer
   x = 886.13