Finding the Fourth Proportional to 1,428.98, 1,971.42 and 839.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,428.98 : 1,971.42 = 839.30 : x
2. Step 2: Convert to fraction form
   1,428.98/1,971.42 = 839.30/x
3. Step 3: Cross multiply
   1,428.98x = 1,971.42 × 839.30
4. Step 4: Simplify right side
   1,428.98x = 1,654,612.81
5. Step 5: Solve for x
   x = 1,654,612.81/1,428.98
6. Step 6: Final answer
   x = 1,157.90