Question

an equation of a line perpendicular to the line represented by the equation y=-1:2x-5 and passing through (6,-4) is

Answer 1

Whatever you intended to type before the 'x' . . . " -1.2 " or " - 1/2 " . . .
that's the slope of the line represented by the equation.

A line perpendicular to it has a slope with the negative reciprocal of this one.
So the perpendicular line would be

y = 0.8333 x (negative reciprocal of -1.2) + any number
or
y = 2 x (negative reciprocal of - 1/2) + any number