Model red cars and solve a zero-or-one probability

A fixed number n of cars is observed and R counts those that are red. (i) State in context two assumptions for a binomial model. Assume now $R\sim B(n,p)$. (ii) For n=20 and p=0.15 find $P(4\le R<8)$. (iii) For n=20 and $P(R=0\text{ or }1)=0.2$, write an equation for p and find p numerically.