Answer
$B=5$
Work Step by Step
It is given, that $f(-1)=12$.
Substituting $x=-1$ into the function $f(x)$ gives:
$f(-1)=3(-1)^2-B(-1)+4$
$12=3(1)+B+4$
$12=3+B+4$
$12=7+B$
Solving this equation for $B$ we get:
$12-7=B\\
5=B$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.