Question

2. -3n(2n – 5) = 0

Answer 1

$-3n(2n-5)=0\iff -3n=0\ \vee\ 2n-5=0\\\\-3n=0\ \ \ |:(-3)\\n=0\\\\2n-5=0\ \ \ \ |+5\\2n=5\ \ \ |:2\\n=\dfrac{5}{2}$

$Answer:\ c.\ n=0\ or\ n=\dfrac{5}{2}$

Answer 2

Altho' it's rather obvious what you're supposed to do here, I'd suggest you always include all of the instructions.

-3n(2n – 5) = 0  is easily solved.  Ignore the coefficient -3.  Then you have n(2n-5)=0  Then either n=0 or 2n=5, which results in n=0 and n = 5/2 (solutions).