A. 84x+7y is bigger than or equal to 70
in example to my post...

(84 x .50 = 42) + (7 x 4 = 28) = 70...
or..
(84 x 1 = 84) + (7 x -2 = -14) = 70...
or....
(84 x .60 = 50.4) + (7 x 4.5 = 31.5) = 81.9

i could just keep going on and on, i was just trying to give you an idea...