He gas state of a substances that is usually a solid or a liquid at room temperature is called a

Water vapor

Explanation:

Water vapor is the gaseous phase of water. Combustion of 1 cubic meter of fuel in a solid fuel furnace produces 0.8 liters of water vapor.

It can be produced by the evaporation of boiling water or the sublimation of ice. Water vapor is water in gaseous instead of liquid form. The water when it's boiling it doesn't disappear, it becomes gas,  ,

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.

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