Answer:
7½×16 in.
Step-by-step explanation:
Data:
11×17 in paper
  ½ in margins
 2½ in column
Calculations:
 Width = 11 - 2 × ½ - 2½ = 11 - 1 - 2½ =  7½ in
Height = 17 - 2 × ½     = 17 - 1     = 16   in
The dimensions of the drawing area are 7½ ×16 in.