We need 3 lines for a triangle. The first one is \(x = -1\) and the second one is \(y = 1\). Now these two lines are perpendicular to each other.

Now the third line is \(y = \frac{-x}{2} + 2.5\).

Now \(x = -1\) and \(y = \frac{-x}{2} + 2.5\) intersect at (-1, 3).

Now \(y = 1\) and \(y = \frac{-x}{2} + 2.5\) intersect at (3, 1).

The third point of the triangle is (-1, 1). So the two sides of triangle is 2 and 4.

Area of triangle is \(\frac{1}{2} * 2 * 4\) = 4

PS: It is easier to solve graphically!