Kinematics 2D: Find Particle's Accel. Vector

[circuscircus]

Homework Statement

A particle moves in the xy plane with constant acceleration. The particle is located at \vec{r} = 2\hat{i} + 4\hat{j} m at t=0s. At t=3s it is at \vec{r} = 8\hat{i} - 2\hat{j} m and has a velocity \vec{r} = 5\hat{i} - 5\hat{j} m/s

What is the particle's acceleration vector a?

Homework Equations

The Attempt at a Solution

Here's what I did
\vec{a} = (\hat{r_{1}} - \hat{r_{2}}) / \Delta t - \vec{r} = 5\hat{i} - 5\hat{j}

The answer is just that without the \vec{r} = 5\hat{i} - 5\hat{j}

Could someone tell me why?

 

[learningphysics]

wait what is the answer?