Finding the Fourth Proportional to 2,100.51, 3,150.78 and 639.69

Step by Step Solution

1. Step 1: Write the proportion equation
   2,100.51 : 3,150.78 = 639.69 : x
2. Step 2: Convert to fraction form
   2,100.51/3,150.78 = 639.69/x
3. Step 3: Cross multiply
   2,100.51x = 3,150.78 × 639.69
4. Step 4: Simplify right side
   2,100.51x = 2,015,522.46
5. Step 5: Solve for x
   x = 2,015,522.46/2,100.51
6. Step 6: Final answer
   x = 959.54