Answer
(a) one-to-one.
(b) $\{(2,1),(5,3),(8,5),(10,6) \}$
Work Step by Step
(a) For the given function, use the horizontal line test, we can see that for each $y$ value, there is only one $x$ value, thus it is one-to-one.
(b) By exchanging $x,y$ values, we can find the inverse as $\{(2,1),(5,3),(8,5),(10,6) \}$