It will be whichever equation you see that has the "c" = +3, in the format:
F(x) = y = ax^2 + bx + c, where a, b, and c are all integers, such that plugging a "0" into the x's will give:
y = a•0^2 + b•0 + 3 = 0 + 0 + 3 = 3
The algebraic property demonstrated in the example below is Transitive Property of Equality. There we can see how the first thing is equal to the second one and notice that the first one is equal to the third one too. This is a Transitive Property of Equality in a nutshel.
Yeah, where I live, to find the slope (or as we call it, the gradient), you just have to do the two y values subtracted from each other, over the two x values subtracted from each other. The important thing is to remember that if you subtract the first y value from the second (so, 12 - 8), you have to do the same thing for the x (6 - 2)

=

= 1.
The slope is 1.
The answer to your question is 30+4.+10+4