If 2^y = 3, then:
(log to the base 2 of) 2^y = (log to the base 2 of) 3
or
y = log to the base 2 of 3
Note that y turns out to be a constant here.
We need to identify the graph that depicts (log to the base 2) of x, and once we have that, draw a vertical line thru x = 3 to estimate y.
Only the 3rd graph qualifies here. Note that all basic log graphs have an x-intercept of (1,0), as the 3rd graph does.
If we draw on the 3rd graph a vertical line thru x=3, we see that this vert. line intersects the curve at roughly y=1.5.