[940+5 (12+ a) -1785] :3+5=410
[940+5 (12+ a) -1785] :3 = 410 - 5
[940+5 (12+ a) -1785] :3 = 405
940+5 (12+ a) -1785 = 405 × 3
940+5 (12+ a) -1785 = 1 215
940+5 (12+ a) = 1 215 + 1 785
940+5 (12+ a) = 3 000
5 ( 12 + a ) = 3 000 - 940
5 ( 12 + a ) = 2 060
12 + a = 2060 : 5
12 + a = 412
a = 412 - 12
a = 400