In slope-intercept form:
y = mx + b
where:
m = slope = -1/3
b = y-intercept = 10/3
y = (-1/3)x + 10/3
However, you want the equation organized in general form, which is:
Ax + By + C = 0
This simply requires us to rearrange terms (starting from slope-intercept form):
y = (-1/3)x + 10/3
(moving all terms to the left)
y - (-1/3)x - 10/3 = 0
y + 1/3x - 10/3 = 0
1/3x + y - 10/3 = 0
For general form:
A = 1/3
B = 1
C = -10/3