Line $l_1$ represents the graph of $3x + 4y = -14$. Line $l_2$ passes through the point $(-5,7)$, and is perpendicular to line $l_1$. If line $l_2$ represents the graph of $y=mx +b$, then find $m+b$.

This is AoPS homework. You should not cheat on your homework.

stop being so annoying I already finished all my hw so yeah. I am just giving people who need the answers the answers