Use the equation y of the second point minus y from the first point all divided by x from the second point divided by x from the first point. Sometimes this is referred to as "change in y" divided by "change in x". In any case you'll get 2-4 or -2 divided by 5-2 or 3. The resulting slope is -2/3. It is important to keep the order of the numbers consistent so that your signs don't get messed up.