Question

y = 2x^2+8x + c is (x, 3) .
state the value of c
still confused on what the value of c is !
help

Answer 1

y = 2x^2+8x + c is (x, 3) 
when x = x, y = 3
so
3 = 2 x^2 + 8 x + c
suspect a typo, need a specific value like (2, 3)
3 = 2* 2^2 + 8 * 2 + c = 8 + 16 + c
3 = 24 + c
c = -21

Answer 2

In your previous posting of this, when you were Dennyelle
you stated that (x,3) was the vertex.
That is critical for the question.
I found the vertex for you to be (-2,3), check back to see

So now that you know that (-2,3) lies on the function....
3 = 2(-2)^2 + 8(-2) + c
3 = 8 - 16 + c
c = 11