Answer
f is not integrable on [3,5].
Work Step by Step
See the definition of a definite integral
(defined as the limit of Riemann sums over partitions $\Delta$).
The first condition is for f TO BE DEFINED on [a,b] = [3,5]
f is not defined on the whole interval, because f is not defined for x=4
(f has a discontinuity on [3,5]),
so
f is not integrable on [3,5]
