if f(x) = x - 7 find the following

f(13) =6
f(-6) =13
f(p) = not sure how to set this one up

Thank you very much

just do what you did with 13 and 6: wherever you see an x, substitute in p:

f(p) = p-7

Not a numeric answer, because you haven't specified what value p has.

f(bozo) = bozo-7
f(40) = 40-7
and so forth.