What equation could I use for this?

[AVReidy]

Homework Statement

Two particles are at the same point at the same time, moving in the same direction. Particle A has an initial velocity of 6.9 m/s and an acceleration of 1.8 m/s2. Particle B has an
initial velocity of 2.4 m/s and an acceleration of 5.7 m/s2.

At what time will B pass A?

Homework Equations

$\Delta$x = v_it + 1/2at²

The Attempt at a Solution

I'm just wondering what equation I should use for this. I think I need to set up a system, but I don't see why I would need displacement for this. The only information the question gives us is v_i for both, the acceleration for both, and the fact that they're going the same direction.

I really don't understand how I would go about solving it. Knowing the equation(s) to use would be a great start!

I'm really discouraged. I just tried setting two equations equal and I got the wrong answer... I don't know what to do.

Thank you so much!

EDIT: I calculated with the quadratic equation wrong somehow, but found the answer.

 

[SammyS]

...

I'm just wondering what equation I should use for this. I think I need to set up a system, but I don't see why I would need displacement for this. The only information the question gives us is v_i for both, the acceleration for both, and the fact that they're going the same direction.
...

One more piece of information.

When B passes A, they're at the same location.