We have
[tex]-2a+7<0 \iff -2a<-7 \iff 2a>7 \iff a>\dfrac{7}{2}=3.5[/tex]
So, for every number greater than 3.5, the function is negative.
In particular, if your domain is the set of integers from 1 to 30, all the integers from 4 to 30, inclusive, will produce a negative result.
