Hello:
the equation is : y = ax+b
the slope is a : a×(1/2) = -1......( perpendicular to a line with a slope of 1/2) because : -2x+4y =8...y=(1/2)x+2 )
a = -2 y=(-2x+b
the line that passes through (2,1) :1 = -2(2)+b
b =5
the equation is : y = -2x+5