To solve the problem, let's define the number of stickers Reann started with as \( x \).
According to the problem, she gives her friend half of her stickers, which leaves her with \( \frac{x}{2} \). Then, her brother gives her 8 new stickers, resulting in:
\[ \frac{x}{2} + 8 = 12 \]
Now we can solve for \( x \):
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Subtract 8 from both sides: \[ \frac{x}{2} = 12 - 8 \] \[ \frac{x}{2} = 4 \]
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Multiply both sides by 2: \[ x = 4 \times 2 \] \[ x = 8 \]
So, Reann started with 8 stickers.
The operations used in this problem are subtraction and multiplication.
Therefore, the correct response is: subtraction and multiplication.