Supply equation. given unit price, quantity, etc.

[rpdrake]

Having problems with this

Supply equation: In economics, one of the standard theories is that of supply and demand. Suppose that in order for suppliers to make 100 widgets per day, the price must be $6, and that in order to make 200 per day, the price must be $7.50. Let x represent the number of items and y represent the price. Write the supply equation.

Nothing that I end up makes sence!
Thanks
A lot!!!!

 

[skeeter]

two ordered pairs ... (100, 6) and (200, 7.5)

rate of change ... (7.5 - 6)/(200 - 100) = 1.5/100 = .015

y - 6 = .015(x - 100)

y - 6 = .015x - 1.5

y = .015x + 4.5

I'm no economist, but it seems to me that in the context of this problem, supply depends on price. solving for x ...

x = (200y - 900)/3