When a line is perpendicular to another line, the gradient becomes the “negative reciprocal” which basically means flip the gradient and change the sign. In this instance the negative reciprocal of 5x has to be -1/5 as it has been flipped and made negative. At this point the answer can only be B or C.
After this you can use the point given to work out the y-intercept:
y-y1 = m(x-x1)
y-3 = -1/5(x+10)
y-3 = -1/5x - 2
y = -1/5x -1
And there’s your answer: C
