[tex]\begin{gathered} a_1=12 \\ a_{25}=a_1+(25-1)d \\ -60=12+24d \\ d=-3 \\ a_n=12+(n-1)(-3) \\ a_n=12-3n+3 \\ a_n=15-3n \end{gathered}[/tex][tex]\begin{gathered} a_n=3=15-3n \\ 3=15-3n \\ 3n=15-3 \\ 3n=12 \\ n=\frac{12}{3} \\ n=4 \end{gathered}[/tex][tex]\begin{gathered} a_8=15-3(8) \\ a_8=-9 \end{gathered}[/tex][tex]\begin{gathered} a_n=-24 \\ -24=15-3n \\ 3n=15+24 \\ 3n=39 \\ n=\frac{39}{3} \\ n=13 \end{gathered}[/tex][tex]\begin{gathered} a_{19}=15-3(19) \\ a_{19}=15-57 \\ a_{19}=-42 \end{gathered}[/tex]
