The easiest way to solve this problem would be to plot it on some graph paper - as you know, in the coordinates given, the first value given is your "x" value - remember the the horizontal axis on your graph is your "x" axis, and the vertical axis is your "y" axis - so to plot these four points, you would set up your graph values by looking at the difference between your highest and your lowest "x" values - i.e. (-70 - lowest, 45 - highest), and then set up a scale on your graph that would work for that range. Do the same thing for your "y" values, and then plot the values. For example, to plot (-70,30), you would go over to the left on your x axis to -70 (since the value is negative - it is plotted to the left of the origin - which is zero. ) Then go up (along the y axis) to 30 to plot the y value. Place a point at this location. Repeat for the other three points and then you will have all four points plotted. Remember that where your x and y axis cross is the origin - or point (0,0). If I could draw a picture this would seem a lot clearer - If you still are confused, I would recommend that you google "rectangular coordinates", and you will find lots of diagrams and explanations for exactly what a rectangular coordinate plane is!
I hope that this helps! Let me know if you have further questions - I'd love to help!