Finding the Fourth Proportional to 1,139.95, 1,573.27 and 642.74

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.95 : 1,573.27 = 642.74 : x
2. Step 2: Convert to fraction form
   1,139.95/1,573.27 = 642.74/x
3. Step 3: Cross multiply
   1,139.95x = 1,573.27 × 642.74
4. Step 4: Simplify right side
   1,139.95x = 1,011,206.55
5. Step 5: Solve for x
   x = 1,011,206.55/1,139.95
6. Step 6: Final answer
   x = 887.07