Finding the Fourth Proportional to 1,428.79, 1,971.71 and 839.21

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.79 : 1,971.71 = 839.21 : x
2. Step 2: Convert to fraction form
   1,428.79/1,971.71 = 839.21/x
3. Step 3: Cross multiply
   1,428.79x = 1,971.71 × 839.21
4. Step 4: Simplify right side
   1,428.79x = 1,654,664.69
5. Step 5: Solve for x
   x = 1,654,664.69/1,428.79
6. Step 6: Final answer
   x = 1,158.09