Problems with solving the dual problem graphically

I have the following problem

minimize $$21x_1-15x_2-16x_3$$

subject to $$2x_1-5x_2+7x_3\ge2$$

$$3x_1+3x_2-2x_3\ge-5$$

$$x_1,x_2,x_3\ge0$$

So, I transformed the second constraint to make sure that the right hand part is positive.

So that made the problem look like this.

minimize $$21x_1-15x_2-16x_3$$

subject to $$2x_1-5x_2+7x_3\ge2$$

$$-3x_1-3x_2+2x_3\le5$$

$$x_1,x_2,x_3\ge0$$

Now the dual problem before the conversion of the second constraint looks like this

maximize $$2y_1=5y_2$$

subject to $$2y_1+3y_2\le21$$

$$-5y_1+3y_2\le-15$$

$$7y_1-2y_2\le-16$$

$$y_1,y_2\ge0$$

But graphically this makes no sense because they don't intercept when both $$y_1,y_2$$ are greater than or equal to zero.

And when I do convert the second constraint I'm not sure how to construct the dual problem.