Suppose nation A can produce 80 units of X by using all its resources to produce X

Question:

Suppose nation A can produce 80 units of X by using all its resources to produce X or 60 units of Y devoting all its resources to Y. Comparable figures for nation B are 60 units of X and 60 units of Y. Assuming constant costs, in which product should each nation specialize? Why? What are the limits of the terms of trade?