From the choice of your answer i figure that you had almost arrived at correct answer, with a minor fault in sign of slope. It was most probably a calculation fault.

Equation of Any line: y =mx + c
c is y intercept. In this question = 3

slope = m = (y2 - y1)/(x2 - x1); where (x1,y1) and (x2,y2) are two points where the line passes

here two points are (0,3) and (6,0)
m = (0-3)/(6-0) = -1/2

eq of line = y = (-1/2)x + 3

any point below that line
y will be less than the equation of line
y<(-1/2)x + 3

Ans E

process with less steps:

y = mx+c

line passes through (0, 3) and (6, 0)

slvign for m and c y = -(1/2)x + c

as someone pointed less than equality will be choosen

so E