Answer
$y=2.954\cdot x^{0.907}$
Work Step by Step
Let $y=ax^b$.
Then our equations are: $8=a3^b$ and $15=a6^b$.
If we divide the second equation by the first one we get:
$1.875=2^b=\\b=\ln_{2}{1.875}\approx0.907$.
Then $8=a3^{0.907}\\a=\frac{8}{3^{0.907}}\approx2.954$.
Thus $y=2.954\cdot x^{0.907}$
