Answer:
Yes, its a linear function.
Step-by-step explanation:
the one that has 65 and 54, 3rd one
So.... notice the picture below
now, we know what the "height" or "altitude" is
now, we also know the perimeter is 18cm
so, k + k + b = 18
or 2k + b = 18
thus

so... one can say that

and you can simplify it if you wish.. not sure you have to