Finding the Fourth Proportional to 1,139.57, 1,572.78 and 667.74

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.57 : 1,572.78 = 667.74 : x
2. Step 2: Convert to fraction form
   1,139.57/1,572.78 = 667.74/x
3. Step 3: Cross multiply
   1,139.57x = 1,572.78 × 667.74
4. Step 4: Simplify right side
   1,139.57x = 1,050,208.12
5. Step 5: Solve for x
   x = 1,050,208.12/1,139.57
6. Step 6: Final answer
   x = 921.59