Collect like terms together and order the terms in descending order of powers of x, the constant being last.
5n²+16n+12=0.
Now we need to factorise: (5n+6)(n+2)=0, so 5n+6=0 making 5n=-6 and n=-6/5; or n+2=0, making n=-2.
So solution is n=-6/5 or -2.