explained answer please

The demand and Supply functions in a competitive market are : 500-sp and Qs = - 40 + 20p respectively The initial Price Po is 100 . Derive the Junction for the time path P and use it to predit price in time period 5 given that the price adjusts is proportion to excess demand at the rate at = 0. 02 ( 9d - Qs). How many time period would you have to wait for the =0 02 to drop by RS 40 . dt