A car is moving with a velocity (3.0 m/s) i^ + (1.0 m/s) j^, and 2.5 seconds later its velocity is (6.0 m/s) i^ - (3.0 m/s) j^ . What is the magnitude of the average acceleration of the car?
a) 2.5 m/s²
b) 3.0 m/s²
c) 4.0 m/s²
d) 5.0 m/s²