Battery Management System (BMS)
$$\Delta Q = I \Delta T$$ right?  You're given

$$
I = 1A \\
\Delta T = 0.5 h \\
\Delta Q = I \Delta T = 0.5 Ah \\
Q_0 = 10 Ah
$$

Thus $$Q_0 - \Delta Q = 9.5 Ah$$  You subtract because of implications of the word "discharge".  Alternatively you could say that the current I is negative.