Data Sufficiency

Can some explain how to work this out please?

First, you should know what you are comparing.

The least height in every class is the greatest height-the range.

So,

for A the least height is g-r

for B, the least height is h-s.

So we have to compare (h-s) with (g-r).

First statement gives us that r<s, but nothing about h and g.

Second statement, gives us that g>h, but nothing about s and r.
So the statements taken separately cannot solve the problem.

If we take both statements, we have that g>h and r<s. Now remember what we are comparing.

They ask you if (g-r)>(h-s). This can be written as g-r-(h-s)>0, or

(g-h)+(s-r)>0. We know that both terms are positive (g>h and s>r), so the sum has to be positive.

We solved the problem using both statements, so both together are sufficient.