AB = 3,5 cm = 35 mm
[tex] \bf \: BC= \frac{1}{5} \times 35 = 7 \: mm[/tex]
A = AB × BC = 35 × 7 = 245 mm²
P = 2 × ( AB + BC ) = 2 × ( 35 + 7 ) = 2 × 42 = 84 mm