Finding the Fourth Proportional to 2,087.61, 3,128.71 and 853.61

Step by Step Solution

1. Step 1: Write the proportion equation
   2,087.61 : 3,128.71 = 853.61 : x
2. Step 2: Convert to fraction form
   2,087.61/3,128.71 = 853.61/x
3. Step 3: Cross multiply
   2,087.61x = 3,128.71 × 853.61
4. Step 4: Simplify right side
   2,087.61x = 2,670,698.14
5. Step 5: Solve for x
   x = 2,670,698.14/2,087.61
6. Step 6: Final answer
   x = 1,279.31