First term, a = - 11

Common difference, a₂ -a = - 8 - (- 11) = 3

Let the last term be a_n

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

49 = - 11 + (n - 1)3

49 + 11 = (n - 1)3

n - 1 = 60/3

n - 1 = 20

n = 21

4^th term from last will be 18^th term from starting

And a₁₈ = a + 17d

= - 11 + 17(3)

= 40

Alternatively we can use the direct formula

a_n = l - (n - 1)d

where, a_n = nth term from last of an AP

l = last term

d = common difference