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 $m+b$.

First you need to figure out the gradient of the first line. Can you do that?

the gradient of the second line is the negative reciprocal of the first, that is m

Sub the pint in to find b

Add m and b together.