Finding the Fourth Proportional to 2,100.87, 3,150.09 and 639.90

Step by Step Solution

1. Step 1: Write the proportion equation
   2,100.87 : 3,150.09 = 639.90 : x
2. Step 2: Convert to fraction form
   2,100.87/3,150.09 = 639.90/x
3. Step 3: Cross multiply
   2,100.87x = 3,150.09 × 639.90
4. Step 4: Simplify right side
   2,100.87x = 2,015,742.59
5. Step 5: Solve for x
   x = 2,015,742.59/2,100.87
6. Step 6: Final answer
   x = 959.48