Three vertices of a rectangle with sides parallel to the axes are $A(3, 1)$, $B(3, 5)$ and $C(7, 5)$. What are the coordinates of the fourth vertex?

Três vértices de um retângulo com lados paralelos aos eixos são $A(3, 1)$, $B(3, 5)$ e $C(7, 5)$. Quais são as coordenadas do quarto vértice?