First term, a = - 5

Common difference,

n = 11

As we know, nth term of an AP is

a_{n =} a + (n - 1)d

where a = first term

a_n is nth term

d is the common difference

a_{11 =} - 5 + (11 - 1)(5/2)

a_{11 =} - 5 + 25

= 20