Answer:
Option d is correct.
Equation : P=7n+20.
Explanation;
Given the perimeter of each figure is;
Perimeter of triangle is equal to the sum of all the sides of a triangle.
Perimeter of 1 triangle is 21
Perimeter of 2 triangle is 34 and
Perimeter of 3 triangle is 41
Let n be the number of figure and P be the perimeter of the figure;
the only equation which satisfy the given perimeter is;

Check:
for n =1 which means 1 triangle then;

for n = 2 , [ i.e 2 triangle]

and for n =3 [i.e, 3 triangles]

Therefore, the equation P =7n+20 relates the number of triangles in the figure(n) to the perimeter of the figure(P).