Finding the Fourth Proportional to 1,139.98, 1,573.22 and 642.59

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.98 : 1,573.22 = 642.59 : x
2. Step 2: Convert to fraction form
   1,139.98/1,573.22 = 642.59/x
3. Step 3: Cross multiply
   1,139.98x = 1,573.22 × 642.59
4. Step 4: Simplify right side
   1,139.98x = 1,010,939.50
5. Step 5: Solve for x
   x = 1,010,939.50/1,139.98
6. Step 6: Final answer
   x = 886.80