In the diagram, each of \triangle Q P T, \triangle Q T S and \triangle Q S R is an isosceles, right-angled triangle, with \angle Q P T=\angle Q T S=\angle Q S R=90^{\circ}. The combined area of the three triangles is 56 . If Q P=P T=k, what is the value of k ?
Answer Choices
A. \sqrt{2}
B. 1
C. 4
D. 2
E. 2\sqrt{2}