⇒ S_{2} = 11

∴ a_{2} = S_{2} – S_{1} = 11 – 4 = 7

**Taking n = 3, we get**

⇒ S_{3} = 21

∴ a_{3} = S_{3} – S_{2} = 21 – 11 = 10

So, a = 4,

d = a_{2} – a_{1} = 7 – 4 = 3

Now, we have to find the 25^{th} term

a_{n} = a + (n – 1)d

a_{25} = 4 + (25 – 1)3

a_{25} = 4 + 24 × 3

a_{25} = 4 + 72

a_{25} = 76

**Hence, the 25**^{th} term is 76.