help pls

$p(q(-1))=4(-1)+7 = 3\\ \text{linear functions are a bijection, i.e. }\\ p(x)=a \text{ and } p(y)=a \Rightarrow x = y\\ p(2)=3 \text{ and } p(q(-1))=3 \Rightarrow q(-1)=2$