Answer :
Given that a ∇ b = 4, it doesn't matter what values you choose for a and b, the result of the ∇ operation is always 4.
So, unless your question is missing some additional details, we have
(4 ∇ 3) ∇ 6 = 4 ∇ 6 = 4
and
(7 ∇ 2) ∇ 5 = 4 ∇ 5 = 4
Given that a ∇ b = 4, it doesn't matter what values you choose for a and b, the result of the ∇ operation is always 4.
So, unless your question is missing some additional details, we have
(4 ∇ 3) ∇ 6 = 4 ∇ 6 = 4
and
(7 ∇ 2) ∇ 5 = 4 ∇ 5 = 4