First we can start off by plugginng in the f(17)
In the function when you plug in a value greater than or equal to 7 you use the formula x + 13,
so your next function is f(f(30)),
you can do the same thing becasue 30 is greater than 7,
so your new function is f(43),
Then you can do this one last time becasue 33 is greater than 7,
and you are left with 56.
f(f(f(17))) = 56