Physics question 5

True.

For example, when you take a direction to be positive, the opposite direction is negative.

Say, let the west direction be positive.
(so that means anything travelling east will be having negative velocity and acceleration)

So, if Car A travelling west is decelerating, it will be having a negative accerleration, because Car A is NOT ACCELERATING in the west direction. Instead, imagine that the resistant force Car A experienced is pushing Car A to the east.

If Car B is travelling east, and is accelerating, it will also have a negative acceleration. As its velocity will be negative,
a = (v-u) / t
a = negative velocity / time
since time is a scalar
a is a negative number