a)
a=10 cm, b=5 cm, O = 220 cm^2
O = 2·(a·b + a·c + b·c)
2·(10·5 + 10·c + 5·c) = 220
2·(50 + 15·c) = 220
100 + 30·c = 220
30·c = 120
c = 4
b)
a = 12 cm, b = 11 cm, O = 540 cm^2
O = 2·(a·b + a·c + b·c)
2·(12·11 + 12·c + 11·c) = 540
2·(132 + 23·c) = 540
264 + 46·c = 540
46·c = 276
c = 6
c)
a = 11,5 cm, c = 9,0 cm, O = 350,5 cm^2
O = 2·(a·b + a·c + b·c)
2·(11.5·b + 11.5·9 + 9·b) = 350.5
2·(103.5 + 20.5·b) = 350.5
207 + 41·b = 350.5
41·b = 143,5
b = 3.5