Finding the Fourth Proportional to 1,139.91, 1,572.91 and 642.55

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.91 : 1,572.91 = 642.55 : x
2. Step 2: Convert to fraction form
   1,139.91/1,572.91 = 642.55/x
3. Step 3: Cross multiply
   1,139.91x = 1,572.91 × 642.55
4. Step 4: Simplify right side
   1,139.91x = 1,010,664.65
5. Step 5: Solve for x
   x = 1,010,664.65/1,139.91
6. Step 6: Final answer
   x = 886.62