Finding the Fourth Proportional to 85.42, 128.25 and 83.15

Step by Step Solution

1. Step 1: Write the proportion equation
   85.42 : 128.25 = 83.15 : x
2. Step 2: Convert to fraction form
   85.42/128.25 = 83.15/x
3. Step 3: Cross multiply
   85.42x = 128.25 × 83.15
4. Step 4: Simplify right side
   85.42x = 10,663.83
5. Step 5: Solve for x
   x = 10,663.83/85.42
6. Step 6: Final answer
   x = 124.84