How to calculate the concentration of NO at equilibrium?
$K_c = \frac{[\ce{NO}]^2}{[\ce{N2}][\ce{O2}]}$

Let x = [NO]

$\frac{x^2}{(0.20M-0.5x)(0.15M-0.5x)} = 0.00041$

$x^2 = 0.00041(0.25x^2 -0.175xM + 0.030M^2)$

$x^2 + 0.000072xM -0.0000123M^2 = 0$