a) n=6,9,12,15,18
b) 12 13 n+1 divizibil cu 4 deci
n+1=16,20,24,28,36
n=15,19,23,27,35
c) 1 3<3n<45
5<3n+2<47
3n+ 2 divizibil cu 5
Deci 3n+2=10,15,20,25,30,35,40
3n=8,13,18,23,28,33,38
Soluții in N : n=6,11
d) 315<5n<=55
19<5n+4<=59
5n+4 divizibil cu 6
5n+4=24,30,36,42,48,54
5n=20,26,32,37,44,50
Soluții in N : n=4 si 10