first thing's first, find the line that's perpendicular to that passes through (-5,-2). since the line is perpendicular, its slope is the negative inverse of the original line, namely, 1/3. now we use the point-slope form to find our line:

now we need to know where these lines meet. so we set them equal to each other:

plug this x-value into either line and you will find the corresponding y-value to be

thus you want to use the distance formula to find the distance between the points (-5,-2) and (5/2, 1/2)

can you continue? perhaps more importantly, do you understand what i did?