Express your answer in scientific notation.

To solve the expression \(2.8 \cdot 10^{-3} - 0.00065\), we first need to convert \(0.00065\) into scientific notation.

We have: \[ 0.00065 = 6.5 \times 10^{-4} \]

Now we can rewrite the expression as: \[ 2.8 \cdot 10^{-3} - 6.5 \cdot 10^{-4} \]

Next, we need a common exponent to subtract these terms. The term \(2.8 \cdot 10^{-3}\) can be rewritten as: \[ 2.8 \cdot 10^{-3} = 28 \cdot 10^{-4} \]

Now substituting this back into our expression gives: \[ 28 \cdot 10^{-4} - 6.5 \cdot 10^{-4} \]

Now, we can combine these since they have the same exponent: \[ (28 - 6.5) \cdot 10^{-4} = 21.5 \cdot 10^{-4} \]

Finally, we need to express \(21.5 \cdot 10^{-4}\) in standard scientific notation. We can convert \(21.5\) to \(2.15\) and adjust the exponent accordingly: \[ 21.5 \cdot 10^{-4} = 2.15 \cdot 10^{1} \cdot 10^{-4} = 2.15 \cdot 10^{-3} \]

Therefore, the final answer in scientific notation is: \[ \boxed{2.15 \cdot 10^{-3}} \]