the question says:

calculate the magnitude and direction of the acceleration of a particle that moves so that its position vector in metres is given by

r=(8t-24^2)i+ (6+4t-t^2)

where t is time in seconds.

I think i have worked out the acceleration to be -4i-2j

and so as a result is the magnitude is 4.47

but i am unsure how to work out direction. My teacher whipped through it and so i got lost... can you help please?