Finding the Fourth Proportional to 2,100.18, 3,149.39 and 639

Step by Step Solution

1. Step 1: Write the proportion equation
   2,100.18 : 3,149.39 = 639 : x
2. Step 2: Convert to fraction form
   2,100.18/3,149.39 = 639/x
3. Step 3: Cross multiply
   2,100.18x = 3,149.39 × 639
4. Step 4: Simplify right side
   2,100.18x = 2,012,457.02
5. Step 5: Solve for x
   x = 2,012,457.02/2,100.18
6. Step 6: Final answer
   x = 958.23