The first thing we can do is to simplify the problem by replacing the expression '10x'. Since we don't know anything about the relationship between x and y, we can replace the expression '10x' with the somewhat simpler expression 'z', and nothing about the problem will change. The rest of this explanation will simply use 'z' in place of '10x'.

We know that both y and z are negative numbers, so we can immediately assume that answers that negate (multiply by -1) the values of y and z will yield greater results than those that don't. So, we can easily eliminate the choice '10x' and the choice '10x+y'.

We also know that z is more negative than y, so -z will be more positive, and therefore greater, than -y. The question now becomes: which is greater, -z or -(z + y)?

Since both z and y are negative, their sum must be more negative than either z or y. Negating the sum of z and y therefore gives a more positive value than either -z or -y. So, now we know that -(z + y) is the answer, or, substituting back in for 'z', the answer is -(10x + y).