Finding the Fourth Proportional to 1,139.76, 1,572.86 and 642.45

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.76 : 1,572.86 = 642.45 : x
2. Step 2: Convert to fraction form
   1,139.76/1,572.86 = 642.45/x
3. Step 3: Cross multiply
   1,139.76x = 1,572.86 × 642.45
4. Step 4: Simplify right side
   1,139.76x = 1,010,480.69
5. Step 5: Solve for x
   x = 1,010,480.69/1,139.76
6. Step 6: Final answer
   x = 886.57