Finding the Fourth Proportional to 85.98, 128.96 and 28.21

Step by Step Solution

1. Step 1: Write the proportion equation
   85.98 : 128.96 = 28.21 : x
2. Step 2: Convert to fraction form
   85.98/128.96 = 28.21/x
3. Step 3: Cross multiply
   85.98x = 128.96 × 28.21
4. Step 4: Simplify right side
   85.98x = 3,637.69
5. Step 5: Solve for x
   x = 3,637.69/85.98
6. Step 6: Final answer
   x = 42.31