Remark
The easiest way to do this is just to find the x and y intercepts when the center of dilation is 0,0 and the scale factor is 1/2
Solution
On the x axis, the value of x is 8 before the dilation takes place. When you dilate by 1/2 x becomes 8*1/2 = 4
On the y axis, the value of y is -6 before the dilation takes place. When you dilate by 1/2, y becomes -6*1/2 = -3
Now join the points (4,0) and (0,-3) That is your new triangle with a dilation of 1/2.