Sketch the vector field $\vec{F}(x,y) = x \vec{j}$, the line segment from $(7,4)$ to $(7,6)$, and the line segment from $(1,7)$ to $(6,7).$
(a) Calculate the line integral of the vector field $\vec{F}$ along the line segment from $(7,4)$ to $(7,6) .$


(b) Calculate the line integral of the vector field $\vec{F}$ along the line segment from $(1,7)$ to $(6,7) .$