Finding the Fourth Proportional to 1,128.72, 1,557.84 and 686.88

Step by Step Solution

1. Step 1: Write the proportion equation
   1,128.72 : 1,557.84 = 686.88 : x
2. Step 2: Convert to fraction form
   1,128.72/1,557.84 = 686.88/x
3. Step 3: Cross multiply
   1,128.72x = 1,557.84 × 686.88
4. Step 4: Simplify right side
   1,128.72x = 1,070,049.14
5. Step 5: Solve for x
   x = 1,070,049.14/1,128.72
6. Step 6: Final answer
   x = 948.02