Sally drives a mini school bus. She starts at the school gate and drives 7 km north for her first pick-up. She then turns right and drives 10 km picking up children along the way. She takes another right turn and drives 5 km. She then takes a final right to return to the school. How far would Sally need to drive to reach back to the school gate again?

The correct option is 12 km.

Let us trace Sally's movement step-by-step from the school gate, considering the starting position as the origin (0, 0):

1. First Leg (North): Sally starts at (0, 0) and drives 7 km North.
Her position becomes (0, 7).

2. Second Leg (East): She turns right (facing East) and drives 10 km.
Her position becomes (10, 7).

3. Third Leg (South): She takes another right turn (facing South) and drives 5 km.
Her position becomes (10, 7 - 5) = (10, 2).

4. Final Leg (Return Path): She takes a final right turn (facing West) to head back toward the school gate at (0, 0).
From position (10, 2), she must drive 10 km West to reach (0, 2), and then 2 km South to reach the school gate at (0, 0).

Therefore, the total distance Sally needs to drive to reach back to the school gate is:

$\text{Total Distance}=10\text{km}+2\text{km}=12\text{km}$