Log2y=1/3(log2 27power)

log₂y  =  (1/3)log₂27

Since a multiplier goes into the log expression as an exponent:

log₂y  =  log₂27^1/3

An exponent of 1/3 represents a cube root, so 27^1/3 = 3  (the cube root fo 27 is 3).

log₂y  =  log₂3

So:  y = 3.