А The perimeter of adjoining rectangle
is 36 cm. If its length is 10 cm, then
find its breadth.

By definition, Perimeter means the sum of the sides. Given that the shape is a rectangle we know that it has two pairs of congruent sides. The difference between the total perimeter and the first pair of sides leaves the sum of the other pair of congruent sides. Since they are congruent then each the second pair must be equal must be the same so algebra at that point:

P_rectangle = side 1 + side2+ side 3+ side 4 given

Side 1= side 2 definition of rectangle

Side 3 =side4 definition of rectangle

P = 36 cm (given)

Let side1 = 10 cm given

Side2 = side 1= 10cm

36 = 10cm + 10cm + side3 +side 4

36= 20 + 2 (side 3)

16 = 2(side 3)

Side 3 = 8

Check to verify

36 = 10+10+8+8

36=36