m is the slope, so when a line is perpendicular to another line is has a slope which is an opposite reciprocal, so change the -1/2 (the slope of the other line) to 2/1 or just 2
so m=2
now you need to plug in the point they give you for x and y
y=mx+b 4=2(4) + b simplify 4=8 + b subtract 8 over -4 = b
now that you know that slope (m) and the y-intercept (b) you can plug those two numbers into the original equation for the answer
