9(x - 2y)2 - 4 (x - 2y) - 13
= 9(2x - 4y) - 4x + 8y - 13
= 18x - 36y - 4x + 8y -13
= 18x - 4x - 36y + 8y -13
= 14x - 28y - 13

Everything that we are surrounded by is known as Environment. They continuously interact with its components and tries to adapt themselves to the conditions in their surroundings. In the environment, there are different interactions between animals, plants, soil, water, and other living and non-living things. It consists of:

• Physical surroundings (air, water, and soil)
• Inorganic substances (carbon dioxide, Nitrogen, water etc.)
• Meteorological factors (temperature, weather, rainfall etc.)

When in an economy aggregate demand falls short of aggregate supply at full employment level, the demand is said to be deficient demand and the gap is called deflationary gap.
Inflationary gap is also referred to as excess demand. When aggregate demand is greater than aggregate supply, at full employment level in the economy, it is referred to as inflationary gap or excess demand. This situation actually results in an increase of prices, that is inflation.

The motion around the sun along its orbit is called a revolution. The amount of time it takes for a single trip around the sun is called a period of revolution. The period for the Earth to revolve around the sun is 365.24 days or one year.