Completes 1.12 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.13 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.14 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.15 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>