Stella divided 12/8.
If we divide 12 by 8, we get exactly 1.5.
Let us check given options one by one .
A) Stella made an error : Stella didn't made an error because it's just division of two numbers.
B) The answer is exactly 1.5. : On dividing 12 by 8, we get exactly 1.5, so this option is correct.
C) The calculator rounded the answer. : On dividing 12 by 8, we get exactly 1.5. So, no rounding is required.
D) The calculator truncated the answer. : On dividing 12 by 8, we get exactly 1.5. So, no truncation in the answer.
Therefore, correct option is B) The answer is exactly 1.5.