The perimeter of a rectangle is calculated with the formula [[$ p = 2(a + b)$]] , where [[$a$]] and [[$ b$]] are the lengths of rectangle's sides. Calculate the perimeter of a rectangle when

a) [[$a = $]] 2.3 cm and [[$b =$]] 4.1 cm.


b) [[$a =$]] 57 mm and [[$b =$]] 23 mm.