Finding the Fourth Proportional to 85.49, 128.42 and 83.21

Step by Step Solution

1. Step 1: Write the proportion equation
   85.49 : 128.42 = 83.21 : x
2. Step 2: Convert to fraction form
   85.49/128.42 = 83.21/x
3. Step 3: Cross multiply
   85.49x = 128.42 × 83.21
4. Step 4: Simplify right side
   85.49x = 10,684.77
5. Step 5: Solve for x
   x = 10,684.77/85.49
6. Step 6: Final answer
   x = 124.99