The recursive rule tells you that
[tex]t_2=t_1+3[/tex]
[tex]t_3=t_2+3=(t_1+3)+3=t_1+2\cdot3[/tex]
[tex]t_4=t_3+3=(t_1+2\cdot3)+3=t_1+3\cdot3[/tex]
and so on, with the general rule
[tex]t_n=t_1+(n-1)\cdot3[/tex]
Then with [tex]t_1=1[/tex], you have
[tex]t_n=1+3(n-1)\implies\boxed{t_n=3n-2}[/tex]