Finding the Fourth Proportional to 10,915.68, 16,375.86 and 3,990

Step by Step Solution

1. Step 1: Write the proportion equation
   10,915.68 : 16,375.86 = 3,990 : x
2. Step 2: Convert to fraction form
   10,915.68/16,375.86 = 3,990/x
3. Step 3: Cross multiply
   10,915.68x = 16,375.86 × 3,990
4. Step 4: Simplify right side
   10,915.68x = 65,339,681.40
5. Step 5: Solve for x
   x = 65,339,681.40/10,915.68
6. Step 6: Final answer
   x = 5,985.86