Finding the Fourth Proportional to 1,139.99, 1,573.29 and 642.71

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.99 : 1,573.29 = 642.71 : x
2. Step 2: Convert to fraction form
   1,139.99/1,573.29 = 642.71/x
3. Step 3: Cross multiply
   1,139.99x = 1,573.29 × 642.71
4. Step 4: Simplify right side
   1,139.99x = 1,011,173.15
5. Step 5: Solve for x
   x = 1,011,173.15/1,139.99
6. Step 6: Final answer
   x = 887.01