pls help me answer this question on micro enonomics?

Question

suppose that the current price of tin is $.75 per
pound and 7.5 million metric tons are sold every year.
The elasticity of demand for tin is -0.8. What is a
linear approximation of the demand for tin?

Answer 1

In math terms, the elasticity of demand is the slope of the line.

That is, for each dollar per pound that the price goes up, the demand decreases by 0.8 million metric tons.

So to find the equation, you can use what is called the point-slope form of an equation:

y - y1 = m(x - x1)

Where (x1, y1) are a particular point that you know (in this case, it would be ($0.75 per pound, 7.5 million metric tons):

The price is the independent variable (x) and the demand is the dependent variable (y):

d - 7.5 = -0.8(x - 0.75) = -0.8x + 0.6

d = -0.8x + 8.1

where d is in millions of metric tons and x is in dollars per pound.