954-77-а=277 помогите

Question

954-77-а=277 помогите

Answer 1

954-77-a=277

877-a=277

a=877-277

a=600

954-77-600=277

277=277

Answer 2

954-77-а=277
954-77=877
877-277=600
___________
954-77-600=277