Răspuns :
-15+8-12+13-9=-15
-15+8=-7
-7-12=-19
-19+13=-6
-6-9=-15
-16+9-13+17-6=-9
-16+9=-7
-7-13=-20
-20+17=-3
-3-6=-9
-15+8=-7
-7-12=-19
-19+13=-6
-6-9=-15
-16+9-13+17-6=-9
-16+9=-7
-7-13=-20
-20+17=-3
-3-6=-9