mathematics sat question

Answer:
A
Step-by-step explanation:
You should simplify this, here [tex]i[/tex] is like a variable.
Now here you just simplify the variables and calculate the numbers.
[tex]7-8 = -1[/tex]
[tex]3i+9i=12i[/tex]
equals
[tex]-1+12i[/tex] which is "A"
I hope it helps you. Please choose my answer as the BRAINLIEST