Answer
We can sketch the vector $a$ and the vector $-c$ so that their initial points coincide. When we complete the parallelogram, the resultant vector through the middle of the parallelogram is the vector $a-c$.
Work Step by Step
To sketch the vector $a-c$, we can sketch the vector $a$ and the vector $-c$ (which points in the opposite direction from the vector $c$) so that their initial points coincide. Then we can use another copy of the vector $a$ and the vector $-c$ to complete the parallelogram. The resultant vector through the middle of the parallelogram is the vector $a-c$.
