Finding the Fourth Proportional to 1,871.72, 2,807.86 and 639.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,871.72 : 2,807.86 = 639.30 : x
2. Step 2: Convert to fraction form
   1,871.72/2,807.86 = 639.30/x
3. Step 3: Cross multiply
   1,871.72x = 2,807.86 × 639.30
4. Step 4: Simplify right side
   1,871.72x = 1,795,064.90
5. Step 5: Solve for x
   x = 1,795,064.90/1,871.72
6. Step 6: Final answer
   x = 959.05