How to do this problem and what's the answer

if a line is perpendicular to another line with slope m, the perpendicular line's slope is always -1/m. Since the slope of the given line is -4, the perpendicular slope would be 1/4 (-1/-4 = 1/4). Our line right now is y = (1/4)x + b. Now substitute the given point in for x and y to solve b. In this case b = -1, so your line would be  y = (1/4)x + -1.

4.28095238095 that is the answer