It it called an equation. Equation consist of number, symbols, and a equal sign.
To solve, first do -2 times t and -2 times 8. Your equation would look like this after: -2T+(-16)=12. Then add 16 to each side. -2T=28. Next, divide by -2. T=-14 is your answer.

and surely you'd know what the roots are
I assume that you meant RS and ST are segments of RT. If that is true then:
RS+ST=RT, using the values for these given...
8y+4+4y+8=36 combine like terms on left side
12y+12=36 subtract 12 from both sides
12y=24 divide both sides by 12
y=2
Answer:
2
Step-by-step explanation:
h(4)=-1
g(h(4))=g(-1)=3
f(3)=2