Answer
$y=28\cdot x^{0.752}$
Work Step by Step
Let $y=ax^b$.
Then two of our equations are: $28=a1^b$ and $64=a3^b$.
Then from the first one: $a=28$
Then $64=28\cdot3^b\\\frac{64}{28}=3^b\\b=\log_3{\frac{64}{28}}\approx0.752$
Thus $y=28\cdot x^{0.752}$
