Finding the Fourth Proportional to 2,103.78, 3,156.15 and 643.05

Step by Step Solution

1. Step 1: Write the proportion equation
   2,103.78 : 3,156.15 = 643.05 : x
2. Step 2: Convert to fraction form
   2,103.78/3,156.15 = 643.05/x
3. Step 3: Cross multiply
   2,103.78x = 3,156.15 × 643.05
4. Step 4: Simplify right side
   2,103.78x = 2,029,562.26
5. Step 5: Solve for x
   x = 2,029,562.26/2,103.78
6. Step 6: Final answer
   x = 964.72