Finding the Fourth Proportional to 1,428.78, 1,972.06 and 839.64

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.78 : 1,972.06 = 839.64 : x
2. Step 2: Convert to fraction form
   1,428.78/1,972.06 = 839.64/x
3. Step 3: Cross multiply
   1,428.78x = 1,972.06 × 839.64
4. Step 4: Simplify right side
   1,428.78x = 1,655,820.46
5. Step 5: Solve for x
   x = 1,655,820.46/1,428.78
6. Step 6: Final answer
   x = 1,158.91