The joint of meat needs to be cooked for 30 minutes per 500 g plus an extra 20 minutes. how long will it take to cook a joint of meat weighting 2.5 kilo grand?

The equation made from this is:
Let x = each 500 grams

Cooking time = 30x + 20

2.5 kg = 2500 grams
2500 / 5 = 5
X = 5

We put this in to the equation,
30*5 + 20 = 170 minutes

It will take 170 minutes to cook a joint of meat weighing 2.5 kilograms