You should use this formula.. d= \sqrt{x} ( x_{2} -  x_{1} )^{2} +(y_{2} - y_{1})^2.. Just substitute the numbers from the variables.. You should use the First point and second. Next the 2nd to the 3rd. Next the 3rd to the fourth and lastly the fourth to the first.. Parallelogram has equal base and its height is also equal.. I suggest draw also the figure in a graphing paper. :)