Unknown values can be taken as anything , for example : the most common is x for unknown values and sometimes, for angles we can take θ(theta).
it is totally upto you!
Answer:
Area of room = 21 * 16
= 336 m²
Area of Carpet = (21 - 1)* (16-1)
= 20*15
= 300
Area of border = Area of room - Area of carpet
= 336 - 300
<h3>= 36 m².</h3>