A sideways opening parabola is in the form

, so we know from the process of elimination that it will either be b or c. Next we have to realize that if the parabola opens to the left it is a negative parabola, just like if a parabola opens upside down it is a negative parabola. So the one that has the negative out front is b.
(7,-3) and (1,-3) The distance of that is 7
(-3,1) and (-3,-2) The distance of that is 3
(-2,8) and (-7,8) The distance of that is 5