Slope is gradient and the formula for this is Y2-Y1/X2-X1

so in the case of the line AB it will be X1=-1 & Y1=2 and X2=2 & Y2=4 so plug those into the formul and you get (4-2)/(2--1) = 2/(2+1) ie 2/3 so gradient/slope = 2/3 and so you just have to do that for the other lines BC, DC and AD and to find it it is a parrallelogram just check if the gradient of AB and DC are equal and if the gradient/slope of BC and AD are equal if they all are then it is a parallelogram and your reason is because because parallel lines have the same gradient/slope