For number 2, all of the statements are correct. If f(x)=x and g(x)=f(2x), then g is twice the slope of f. Since both of them have a b value of 0, they both have the same y-intercept. When the b is 0 then the line crosses the origin.
For number 3 it’s A because when the equation is y=-3 it means that there’s a straight horizontal line going through the point (0,-3), thus the slope is 0. This equation can be looked at as y=0x-3 because the -3 is the b.
If the equation was x=-3 then there would be a straight vertical line going through the point (-3,0)
Hope this helps!