to get the distance from (0,0) to (5,0)
as these points are both on the horizontal x-axis
so the distance is 5-0=5.
The x and y axes are perpendicular.
Hence you want the distance from (2,3) to (2,0) as the perpendicular height,
which is 3.
Now you can use the area of a triangle = half the base times the height.