Помогите с 1,2,3 4 сам разобрался

1)
$\frac{x}{3} + \frac{x}{12} = - 5 \\ 4x + x = - 60 \\ 5x = - 60 \\ x = - 60 \div 5 = - 12$
2)
$4c(c - 2) - {(c - 4)}^{2} = 4 {c}^{2} - 8c - {c}^{2} + 4c - 16 = 3 {c}^{2} - 4c - 16 = 3 \times {( - 3)}^{2} - 4 \times ( - 3) - 16 = 27 + 12 - 16 = 23$
3)
$\frac{x}{a} - \frac{ {x}^{2} - {a}^{2} }{ {a}^{2} } \times \frac{a}{x + a} = \frac{x}{a} - \frac{(x - a)(x + a)}{a} \times \frac{1}{x + a} = \frac{x}{a} - \frac{x - a}{a} = \frac{x - (x - a)}{a} = \frac{x - x + a}{a} = \frac{a}{a} = 1$