What is the area of triangle QRS?
7 square units
9 square units
10 square units
13 square units

Circumscribing a rectangle around the triangle SQR, as shown in the figure, we see that the rectangle has dimensions 3 by 6, so its area is 18 square units.

We can also see that the area between the rectangle and the triangle SQR consists of 3 right triangles with dimensions 2 by 3; 6 by 2, and 1 by 4.

The area of there 3 triangles is (2*3)/2 + (6*2)/2 +(1*4)/2 = 3+6+2=11. 

Thus, the area of the triangle is what is left from removing the areas of the 3 surrounding triangles from the area of the rectangle:

A(SQR)=18-11=7 (square units).

7 square units