Here, First term = a = - 40

Common difference = d = - 15 - (-40) = 25

To find = 15^th term, ∴ n = 15

Using the formula for finding n^th term of an A.P.,

a_n = a + (n - 1) × d

∴ a_n = - 40 + (15 - 1) × (25)

⇒ a_n = - 40 + 14 × (25) = - 40 + 350 = 310

∴ 15^th term of the given AP is 310.