How to solve this math question ? Someone can show equation for me?

A wilderness hiker must pack three items : food , first-aid kits,and clothes.The backpack has a capacity of 3kg.Each unit of food takes 1/2kg. A first-aid kit occupies 1/4kg and each piece of cloth takes about 1/2kg . The hiker allocates the clothes to be one unit more than the total units of food and first-aid kit as clothes are the most valuable of the three items. From experience, he knows that total units of first-aid kit must be twice more than the food. How many of each item should he take ?