Finding the Fourth Proportional to 2,105.20, 3,156.28 and 643.56

Step by Step Solution

1. Step 1: Write the proportion equation
   2,105.20 : 3,156.28 = 643.56 : x
2. Step 2: Convert to fraction form
   2,105.20/3,156.28 = 643.56/x
3. Step 3: Cross multiply
   2,105.20x = 3,156.28 × 643.56
4. Step 4: Simplify right side
   2,105.20x = 2,031,255.56
5. Step 5: Solve for x
   x = 2,031,255.56/2,105.20
6. Step 6: Final answer
   x = 964.88