Question

what is wrong in my step

Answer 1

yes,
49p^2+4+28p-4(14p^2+p-3)=0
49p^2+4+28p-56p^2-4p+12=0
-7p^2+24p+16=0
is your answer

Answer 2

check your last step you have written 3 on last it would be 12 you forgot to multiply 3 with 4