If the tangent to the curve $y^2+3x-7=0$ at the point (h, k) is parallel to the line $x-y =4, $ then the value of k is :

$-\frac{2}{3}$ $-\frac{3}{2}$ $\frac{3}{2}$ $\frac{2}{3}$

$-\frac{3}{2}$