[tex]\displaystyle\bf\\64a^{4} b^{8} m^{2} =y^{2} \\\\\\8^{2} \cdot(a^{2} )^{2} \cdot(b^{4} )^{2} \cdot m^{2} =y^{2}\\\\\\\Big(8a^{2}b^{4} m\Big)^{2} =y^{2} \\\\\\\boxed{y=8a^{2} b^{4}m}[/tex]