مسألتين

[م.م.معالي]

The amount of solid waste (W) generated every year in a given country is estimated in millions of tons.  This amount was 140 in the year 1980, and 180 in the year 2000.  Assuming that the amount of waste generated is a linear function of time ,

(i)   Find the equation describing the function W(t).             
(ii)  Find the amount of waste expected in the year 2005.          
 (iii)  In what year will the amount of waste be 300 millions of tons.