Answer
$2$
Work Step by Step
$\int^4_0 \int^{(\frac{y}{2})-1}_{y/2} (x-\dfrac{y}{2}) \space dx \space dy =\int^4_0 [\dfrac{x^2}{2}-\dfrac{xy}{2}]^{\dfrac{-y}{2}+1}_{\dfrac{y}{2}} dy$
or, $=\dfrac{1}{2}\int^4_0 [(\dfrac{y}{2}+1)^2-(\dfrac{y}{2})^2-(\dfrac{y}{2}+1)y+(\dfrac{y}{2})] dy$
or, $=\dfrac{1}{2} \times \int^4_0 (y+1-y)dy $
or, $=\dfrac{1}{2} \times \int^4_0 (1) dy $
or, $=\dfrac{1}{2} \times 4$
or, $=2$
