Finding the Fourth Proportional to 2,139.78, 3,212.85 and 1,315.68

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.78 : 3,212.85 = 1,315.68 : x
2. Step 2: Convert to fraction form
   2,139.78/3,212.85 = 1,315.68/x
3. Step 3: Cross multiply
   2,139.78x = 3,212.85 × 1,315.68
4. Step 4: Simplify right side
   2,139.78x = 4,227,082.49
5. Step 5: Solve for x
   x = 4,227,082.49/2,139.78
6. Step 6: Final answer
   x = 1,975.48