Ok since your given two points of (-5,2) and origin which is always (0,0) you can find the slope with this formula of y2-y1/x2-x1 plug them in the formula and you should get 0-2/0-5 which is equal to -2/-5 or 2/5 negative signs cancel out now you found your slope but remember the promblem was asking for perpendicular slope to get this you simply flip or reciprocate the slope and take take the opposite sign in our case the slope is 2/5 but the perpendicular version is -5/2 hope this helps.
