Explicație pas cu pas:
x este număr naturap, deci poate fi un număr de la 0 la 9.
=>A={12,13,14,15,16,17,18,19,20,21}
A={12,13,14,15,16,17,18,19,20,21}B={15,19,23,27,31,35,39,43,47,50}
A={12,13,14,15,16,17,18,19,20,21}B={15,19,23,27,31,35,39,43,47,50}C={10,13,16,19,22,25,28,31,34,37,40}