The break even point is when profit is equal to zero, or in this case when p(x)=0
4x^2-28x+40=0
4(x^2-7x+10)=0
4(x^2-2x-5x+10)=0
4(x(x-2)-5(x-2))=0
4(x-5)(x-2)=0
So the break even points are when x=2 and 5, which is when 2000 and 5000 units are sold.