Finding the Fourth Proportional to 1,139.89, 1,573.10 and 642.58

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.89 : 1,573.10 = 642.58 : x
2. Step 2: Convert to fraction form
   1,139.89/1,573.10 = 642.58/x
3. Step 3: Cross multiply
   1,139.89x = 1,573.10 × 642.58
4. Step 4: Simplify right side
   1,139.89x = 1,010,848.14
5. Step 5: Solve for x
   x = 1,010,848.14/1,139.89
6. Step 6: Final answer
   x = 886.79