```

a = (v_f - v_i) / t

```

where:

* `a` is acceleration in meters per second squared (m/s²)

* `v_f` is the final velocity in meters per second (m/s)

* `v_i` is the initial velocity in meters per second (m/s)

* `t` is the time in seconds (s)

In this case, the car goes from 20 m/s to 30 m/s in 10 seconds. So, the initial velocity is 20 m/s, the final velocity is 30 m/s, and the time is 10 seconds. Plugging these values into the formula, we get:

```

a = (30 m/s - 20 m/s) / 10 s

```

```

a = 1 m/s²

```

Therefore, the car accelerates at a rate of 1 m/s².