500 - [(245 ÷ 5 + 5 × m) ÷ 9 + 89] = 400
(245 ÷ 5 + 5m) ÷ 9 + 89 = 500 - 400
(49 + 5m) ÷ 9 + 89 = 100
(49 + 5m) ÷ 9 = 100 - 89
(49 + 5m) ÷ 9 = 11
49 + 5m = 11 × 9
49 + 5m = 99
5m = 99 - 49
5m = 50
m = 50 ÷ 5
m = 10
