Modelling the reality

The perimeter of an equilateral triangle which side measures x:

There are x cars in a parking. The amount of wheels is:

A person's age, in algebraic language, ten years ago, being x his/her actual age:

The price, in €, of x kilos of pears that costs 1.45€ per kilogram:

The double of a number plus three, in algebraic language, will be...