perim.drept = 2L +2l =p
perim. patrat = 4· 22,5 = 90 cm
l= 2/7 · L
p= 2L + 2l = 2L + 2· 2/7 ·L = 2L + 4L /7 = ( 2L· 7 + 4L) /7= 18L /7
18L /7 = 60% · 90 = 60 /100 · 90 = 5400/100= 54
18L /7 =54 ; 18L= 7· 54 ; L= 7 · 54 : 18 =21 cm
l= 2 / 7 · L= 2/7 · 21 = 42 /7 =6cm