if in the expansion of (a+b)^n and (a+b)^n+3 the ratio between second and third and third and fourth terms respectively are equal , then n equals----

Dear student

The equations are

nC2 (a)^2 b ^(n-2). / (n+3)C2 (a)^2 b^(n+1) = r

Similarly for nc3 and (n+3) c3 and fourth term

Simplify the ratio to find n

Regards