The first and seventh terms of an arithmetic progression are -11 and 13 respectively. Find the common difference, d, and the nth term.

Given $a_1 = -11$ and $a_7 = 13$. Substitute these values into the formula for $a_7$:

$$a_7 = a_1 + (7-1)d$$ $$13 = -11 + 6d$$

$$13 + 11 = 6d$$ $$24 = 6d$$ $$d = \frac{24}{6}$$ $$d = 4$$

The common difference is $\boxed{4}$.

Substitute $a_1 = -11$ and $d = 4$ into the formula:

$$a_n = -11 + (n-1)4$$

$$a_n = -11 + 4n - 4$$ $$a_n = 4n - 15$$

The $n$-th term is $\boxed{4n - 15}$.