Finding the Fourth Proportional to 1,139.89, 1,573.03 and 642.57

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.89 : 1,573.03 = 642.57 : x
2. Step 2: Convert to fraction form
   1,139.89/1,573.03 = 642.57/x
3. Step 3: Cross multiply
   1,139.89x = 1,573.03 × 642.57
4. Step 4: Simplify right side
   1,139.89x = 1,010,778.67
5. Step 5: Solve for x
   x = 1,010,778.67/1,139.89
6. Step 6: Final answer
   x = 886.74