Completes 1.16 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.17 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.18 exercise

Signed-off-by: Irina Chichikova <diva.artim@gmail.com>
Completes 1.19 exercise

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