Microeconomic – Trade policy

I don’t understand this Economics question and need help to study.

please assist with the attached questions in detail, thank you !!

In this question, we study the consequences of trade policies on the automobile market. We assume that cars are all similar on the market (in other words, a car is a homogeneous good). The supply of Japanese cars is perfectly elastic at a price pJ = 20. Moreover, the supply of cars made in the US is QSus = p − 15 for any price larger than 15. Finally, the demand for cars from American consumers is QD = 30 − 1/2p