You can do this step by step.
First roll can be any and you can still get the correct outcome.
Second roll has to be different from the first one, that is 5/6
3rd roll will have to be different from the last two, that is 4/6
And so on.
Thus P=1*5/6*4/6*3/6*2/6*1/6, you can simplify this if you wish.
The symbol "<=" without quotes means "less than or equal to"
-6x + 2y <= 42
-6x + 2y + 6x <= 42 + 6x ... Add 6x to both sides
2y <= 6x + 42
2y/2 <= 6x/2 + 42/2 ... divide every term by 2
y <= 3x + 21
So the answer is choice D
if the diameter is 8 units, then the radius is half that or 4.