Finding the Fourth Proportional to 2,100.72, 3,150.53 and 639.89

Step by Step Solution

1. Step 1: Write the proportion equation
   2,100.72 : 3,150.53 = 639.89 : x
2. Step 2: Convert to fraction form
   2,100.72/3,150.53 = 639.89/x
3. Step 3: Cross multiply
   2,100.72x = 3,150.53 × 639.89
4. Step 4: Simplify right side
   2,100.72x = 2,015,992.64
5. Step 5: Solve for x
   x = 2,015,992.64/2,100.72
6. Step 6: Final answer
   x = 959.67