Here n = 7 so there would be two middle terms given by

Now

For T₄ , r= 3

The term will be

T_r+1 = ⁿC_r a^n-r b^r

For T₅ term , r = 4

The term T_r+1 in the binomial expansion is given by

T_r+1 = ⁿC_r a^n-r b^r