If 3x+7=x2+p=7x+5 , what is the value of P ?

$3x+7=7x+5=>7x-3x=2=>4x=2=>x=2$

Now,  $3x+7=x2+p=\frac{3}{2}+7=\frac{1}{4}+p=>p=\frac{17}{2}$