Verified answer

[tex] \frac{ {4a}^{2} - {b}^{2} }{10a - 5b} = \frac{(2a - b)(2a + b)}{5(2a - b)} = \frac{2a + b}{5} \\ a = - 2 \: \: \: \: \: b = - 1 \\ \frac{2 \times ( - 2) - 1}{5} = \frac{ - 4 - 1}{5} = - \frac{5}{5} = - 1[/tex]