Can anyone help me I don’t understand plz

There we have an information of two functions [tex] g(t)\, and \, h(t) [/tex]
Using this two functions [tex] g(t)\, and \, h(t) [/tex], we need to find the composition of functions (h\circ g)(t).
The composition of two functions h and g is the new function , by performing g first and then performing h.
[tex] (h\circ g)(t)=h(g(t)) [/tex]
[tex] g(t)=3(t+1) [/tex]
[tex] h(t)=2t [/tex]
Composition of h and g (t) = [tex] (h\circ g)(t) [/tex]
[tex] =h(g(t)) [/tex]
First plugin the value of [tex] g(t)=3(t+1) [/tex]
[tex] h(g(t))=h(3(t+1)) [/tex]
[tex] =h(3t+3) [/tex]
We know that [tex] h(t)=2t [/tex], we need to find h(3t+3),
That is, to replace t by 3t+3,
[tex] =2(3t+3) [/tex]
Now distribute 2 into 3t+3,
[tex] =6t+6 [/tex]
Now plug in [tex] t=-6, [/tex]
[tex] h(g(-6))=6(-6)+6 [/tex]
[tex] =-36+6
\\ =-30 [/tex]
Thus the solution is (D). [tex] h(g(-6))=-30. [/tex]