Grand Forks Homes, Inc. v. State, 2011 ND 65, ¶ 20, 795 N.W.2d 335. "Subject matter jurisdiction cannot be waived and can be raised sua sponte at any time in a proceeding." S&B Dickinson Apartments I, LLC v. Stark Cty. Bd. of Comm'rs, 2018 ND 158, ¶ 5, 914 N.W.2d 503. "When jurisdictional facts are not disputed, the issue of subject matter jurisdiction is a question of law, which we review de novo." IRET Props. LP v. Williams Cty. Bd. of Comm'rs, 2018 ND 223, ¶ 3, 918 N.W.2d 56.

"Statutory interpretation is a question of law." S & B Dickinson Apartments I, LLC v. Stark Cty. Bd. of Comm'rs , 2018 ND 158, ¶ 10, 914 N.W.2d 503. A

We summarily affirm the district court's judgments of dismissal under N.D.R.App.P. 35.1(a)(7). See S&B Dickinson Apartments I, LLC v. Stark Cty. Bd. of Comm'rs, 2018 ND 158, ¶ 22, 914 N.W.2d 503 ("Service of the notice of appeal on the state tax commissioner within thirty days is necessary to perfect an appeal from a board of county commissioners' decision relating to taxation."). [¶2]

Id. See also S&B Dickinson Apts. I v. Stark Cnty. Bd. of Comm’rs , 2018 ND 158, ¶ 22, 914 N.W.2d 503 (within 30 days of order taxpayer must file notice of appeal with the district court, and serve the notice on the Board and State Tax Commissioner). [¶ 4] Here, the Board’s decision denying the taxpayers’ applications was made on February 21, 2017.