Let the line p be the perpendicular bisector of A = (24, 7) and B = (3, 4). Given that AB meets p at C = (x, y), what is 2x - 4y.

2x - 4y = -7.

If C is half-way between (24, 7) and (3, 4) then it has coordinates ( (24+3)/2, (7+4)/2 )   so x = 27/2  and y = 11/2,

Hence 2x - 4y = 27 - 22 = 5