You can
put this solution on YOUR website!What you have done so far looks right.
20x + 10 <= -1/2y
Now multiply both sides by -2, which of course reverses the inequality sign:
-2(20x + 10) >= -2(-1/2y)
-40x - 20 >= y
You probably don't want y on the right side so switch sides, but when you do this reverses the inequality again:
-40x - 20 >= y
y<=-40x-20
Is that what you wanted to do??
R^2 at SCC