**Solution:**

**(i) **Given,

First term, a = 7

Common difference, d = 3

Number of terms, n = 8,

We have to find the nth term, a_{n} = ?

As we know, for an A.P.,

a_{n} = a + (n −1) d

Putting the values,

⇒ 7 + (8 − 1) 3

⇒ 7 + (7) 3

⇒ 7 + 21 = 28

Hence, a_{n} = 28

**(ii)** Given,

First term, a = -18

Common difference, d = ?

Number of terms, n = 10

nth term, a_{n} = 0

As we know, for an A.P.,

a_{n} = a + (n − 1) d

Putting the values,

0 = − 18 + (10 − 1) d

18 = 9 d

d = 18/9 = 2

Hence, common difference, d = 2

**(iii)** Given,

First term, a = ?

Common difference, d = -3

Number of terms, n = 18

Nth term, a_{n} = -5

As we know, for an A.P.,

a_{n} = a +(n − 1) d

Putting the values,

−5 = a + (18 − 1) (−3)

−5 = a + (17) (−3)

−5 = a − 51

a = 51 − 5 = 46

Hence, a = 46

**(iv)** Given,

First term, a = -18.9

Common difference, d = 2.5

Number of terms, n = ?

Nth term, a_{n} = 3.6

As we know, for an A.P.,

a_{n} = a +(n −1) d

Putting the values,

3.6 = − 18.9+(n − 1)2.5

3.6 + 18.9 = (n − 1)2.5

22.5 = (n − 1)2.5

(n – 1) = 22.5/2.5

n – 1 = 9

n = 10

Hence, n = 10

**(v)** Given,

First term, a = 3.5

Common difference, d = 0

Number of terms, n = 105

Nth term, a_{n} = ?

As we know, for an A.P.,

a_{n} = a + (n − 1) d

Putting the values,

a_{n} = 3.5 + (105 − 1) 0

a_{n} = 3.5 + 104 × 0

a_{n} = 3.5

Hence, a_{n} = 3.5