Hello aspirant,

Formula: tn= a+ (n-1)d

Now,

t7= a+ (7-1)d

-4= a+ 6d --(1)

t13= a+ (13-1)d

-16 = a+ 12d -- (2)

we can write eqs 1 and 2 as,

eq 1: a+6d+4=0 and eq 2: a+12d+16=0

subtract (1) from (2) we get,

(a+12d+16)-(a+6d+4) = 0

Therefore,

6d + 12 = 0

6d = - 12

d = - 2

Now, putting the value of 'd' in equation (1) we get,

-4 = a + 6x-2

-4= a - 12

a= 12- 4

a= 8

Hence,  A.P. is 8, 6, 4 , 2

Thank you.