Question

-np-90<30 solve for n

Answer 1

-np - 90 < 30

Add 90 to each side, since we have to do everything on one side so we can solve the unknown variable. 
$-np \ \textless \ 30 + 90$

Simplify/add 30 + 90, which should equal 120.
$-np \ \textless \ 120$

Divide each side by p, which should create a fraction due to the division.
$-n \ \textless \ \frac{120}{p}$

Our last step is to multiply each side by -1. We got negative 1 since a variable by itself can be considered the number 1, and since it had a negative sign in front of it.
$n \ \textgreater \ -\frac{120}{p}$

Answer: $n \ \textgreater \ - \frac{120}{p}$

Answer 2

$-np-90\ \textless \ 30\\\\-np -90 +90\ \textless \ 30 + 90\\\\-np \ \textless \ 120\\\\\frac{-np}{-p}\ \textless \ \frac{120}{-p}\\\\\boxed{\bf{n \ \textgreater \ -\frac{120}{p}}}$

Note: When you divide by a negative answer on both sides, you have to flip the sign.