a)
[tex]x \\ x + 3 \\ - 5(x + 3) = - 5x - 15[/tex]
[tex]f(x) = - 5x - 15[/tex]
b)
[tex]f( - 3) = - 5( - 3) - 15 = 15 - 15 = 0[/tex]
[tex]f(4) = - 5 \times 4 - 15 = - 20 - 15 = - 35[/tex]
[tex]f ( - 5) = - 5( - 5) - 15 = 25 - 15 = 10[/tex]
c)
[tex]f(x) = - 12 \\ - 5x - 15 = - 12 \\ 5x + 15 = 12 \\ 5x = 12 - 15 = - 3 \\ x = \frac{-3}{ 5} = - \frac{3}{5} [/tex]