hello:
Increase in length is : (30×10)/100 =3 cm
Increase in width is : (20×5)/100 = 1 cm
the new length is : 30 cm+3cm =33 cm
the new width is : 20cm+1 cm =21 cm
the perimeter is : 2(20+30) = 100 cm
the new perimeter is : 2(33+21) = 108 cm
the pourcentage increase in the perimetr is : 8%
108 =100/100+8/100=1+8/100