$\text{a)}{y}_{\max }=f\left(-7\right)=3$  

$y_{\min }=f\left(-2\right)=-4$  

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$\text{b)}{y}_{\max }=f\left(4\right)=2$  

$y_{\min }=f\left(0\right)=-2$  

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$\text{c)}{y}_{\max }=f\left(4\right)=2$  

$y_{\min }=f\left(-2\right)=-4$