Finding the Fourth Proportional to 2,087.70, 3,128.79 and 915.94

Step by Step Solution

1. Step 1: Write the proportion equation
   2,087.70 : 3,128.79 = 915.94 : x
2. Step 2: Convert to fraction form
   2,087.70/3,128.79 = 915.94/x
3. Step 3: Cross multiply
   2,087.70x = 3,128.79 × 915.94
4. Step 4: Simplify right side
   2,087.70x = 2,865,768.27
5. Step 5: Solve for x
   x = 2,865,768.27/2,087.70
6. Step 6: Final answer
   x = 1,372.69