standard form means, move the variables to the left-hand-side and leave the constant all by herself on the right-hand-side, usually sorting the variables, so"x" goes first.
now, there's a denominator, we can do away with it, by simply multiplying both sides by the denominator, so let's do so,
[tex]\bf y=-\cfrac{2}{3}x+7\implies \boxed{3}\cdot y=\boxed{3}\cdot \left( -\cfrac{2}{3}x+7 \right)\implies 3y=-2x+21
\\\\\\
\stackrel{standard~form}{2x+3y=21}[/tex]
