391p^2 +160p − 399

What do you want to do with this?     You cannot solve for 'p' because there is no ' = ' since in your expression.....

391p^2  + 160p  - 399

Factors  of 391 we can maybe use  = 17 , 23

Factors  of  399 we can maybe use  =  3, 7 , 19, 21, 57, 133

So  we  can test these to see which  gives us   160 p

(23  p  +  19) ( 17p - 21)  =   no

(23 p  + 21) ( 17 p - 19)  =  no

(23p - 19) (17 p + 21)  =  391p^2 + 23*21p - 21*19p  - 399  =  391 p^2 + 160p  - 399