I think its b but im not sure
To find the equivalence you need to simplify the expression to get
84x - 16y - 10.6
:)))
-6 x -4 = 24
24/-6 = -4
24/-4 = -6
Hope this helps :)
You find a parallelogram area by this formula:

Where
b is its base and
h, its height.
You get
b's value applying distance between two points formula.
If A and B points form the base:

And
h is the perpendicular distance between both bases.
You can visit next link to know further about it:
https://www.ck12.org/geometry/Distance-Between-Parallel-Lines/lesson/Distance-Between-Parallel-Lines
-GEOM/
And in attached picture you can find an example in progress you may want to finish.