put the equation 2x - y = 16 in the form of y = mx + c
2x - y = 16
2x = 16 + y
y = 2x - 16
the slope of this line is 2. the slope of a line perpendicular to it would be the negative reciprocal of 2. in other words, it would multiply with 2 to give -1.
you can form this equation with that info
2x = -1
x = -1/2
OR
you can flip and change the sign (numerator) of 2/1
2/1
= -1/2