If one entity touch another do?

Hello, could you please help me? I just want to do a code in addon, that gives money, if one entity touch another? For example, i have meth addon, but it sells with way, which is - Taking meth and then USE on seller, but i want a way, that force you to bring it in gravity gun or inventory to seller and to sell it only near seller, yes
How can i realize it? Money giving from seller depends from lbs of meth you gived him

Try taking a look at these

http://wiki.darkrp.com/index.php/Functions/Player/Server/addMoney

You’ll have to overwrite the Use function that the addon uses by default.