Determine the following limits $($if they exist$).(2$ marks each$)$

a$.\underset{x3}{lim}(3x^{4}2x^2-5)$

b$.\underset{x5}{lim}(\frac{4x}{x-5})$

c$.\underset{x4}{lim}(\frac{x^{3}x-22}{8-2x})$