The most stable community in an
ecosystem at that time is referred to
as

A climax community refers to a stable ecosystem in its final stage of ecological succession. Succession is when one community of plants and animals replaces another in an ecosystem. In a climax community, the plants and animals are in balance with each other and their environment.

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

: -)