1). 90 : i =3 (rest 2) ↔ 90 = 3 i + 3 ↔ 3 i = 87 ↔ i = 87: 3 = 29
2). ____ ____
2 | x13x ↔ x={2;4;6;8} → x13x = {2132 ; 4134 ; 6136 ; 8138}
3) a + a+2 + a+4 =198 ↔ 3a=198-6 ↔ 3a=192 ↔ a=64 → R: 64;66;68
4) f= nr.fete si b=nr.baieti ; stiim ca b=2×f
daca b-14 = f+28 ↔ 2f-14=f+28 ⇒ 2f-f = 28+14
↓
f = 42 → b= 2×42 = 84