3. For the systems below, x(t) is the input while y(t) is the output. Determine whether each system is linear or nonlinear. Fully justify your answer for each system. \text { (a) } \frac{d}{d x} y(t)+2 \cdot y(t)=x^{2}(t) \text { (b) } \frac{d}{d t} y(t)+3 t \cdot y(t)=t^{2} \cdot x(t) \text { (c) } 3 \cdot y(t)+2=x(t) \text { (d) } \frac{d}{d t} y(t)+y^{2}(t)=x(t)

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