Let point O(0, 0) represent origin which is a null vector at origin in coordinate plane.
Define vector u = OC + OD and vector v = OD + OE
Algebraically vector OC = -2i + 5j , vector OD = 3i + 8j and vector OE = 4i - 1j
here i and j are unit vectors in x & y directions respectively.
Therefore vector u = (-2+3)i + (5+8)j = 1i + 13j and vector v = (3+4)i + (8-1)j = 7i + 7j
Determine vector u + v by adding respective components i and j we get
Vector u + v = (1+7)i + (13+7)j = 8i + 20j
I plotted these vectors u, v and u + v on a graph paper. They match.