a)

[tex] \frac{ {m}^{2} - 12}{m - 4} - \frac{4}{m - 4} = \frac{ {m}^{2} - 12 - 4 }{m - 4} = \frac{ {m}^{2} - 16 }{m - 4} = \frac{(m - 4)(m + 4)}{m - 4} = m + 4[/tex]

[tex] - 2 + 4 = 2[/tex]

b)

[tex] \frac{5k + 11}{ {k}^{2} - 9 } - \frac{4k + 14}{ {k}^{2} - 9} = \frac{5k + 11 - 4k - 14}{ {k}^{2} - 9 } = \frac{k - 3}{ (k - 3)(k + 3) } = \frac{1}{k + 3} [/tex]

[tex] \frac{1}{ - 2.8 + 3} = \frac{1}{0.2} = 5[/tex]