Sharonda uses a blend of dark chocolate and milk chocolate to make the ice cream topping at her restaurant. She needs to buy 120
 
kg
120kg120, start text, k, g, end text of chocolate in total for her next order, and her recipe calls for twice the amount of dark chocolate as milk chocolate.
Let
d
dd be the number of kilograms of dark chocolate she buys and
m
mm be the number of kilograms of milk chocolate she buys.