The gradient is another term for slope. Where slope, m, equals (y2-y1)/(x2-x1).
(0,-5) => (x1,y1)
(6,3) => (x2,y2)
Now plug into the formula,
m=(3-(-5))/(6-0) => (3+5)/(6-0) => 8/6 => 4/3
Thus, the gradient (slope) of the line passing through the two given points is, m=4/3