Table:
0
A
B
C
D
1
Year Ended December 31,
Change
2
2018
2017
Percent
3
(in thousands)
4
Service revenue
$520,193
$485,175
7.2%
5
On-net revenues
374,555
346,445
8.1%
6
Off-net revenues
145,004
137,892
5.2%
7
Network operations expenses(1)
219,526
209,278
4.9%
8
Selling, general, and administrative expenses(2)
133,858
127,915
4.6%
9
Depreciation and amortization expenses
81,233
75,926
7.0%
10
Gains on equipment transactions
982
3,862
(74.6)%
11
Interest expense
51,056
48,467
5.3%
12
Income tax expense
12,715
25,242
(49.6)%

Questions and formulas:
Question: What is the average service revenue earned by the company in 2017 and 2018?
Formula: (C4 + B4)/2 
Formula2: (C4 + B4)/2 
Level: Calculation
Question: What is the average on-net revenue earned by the company in 2017 and 2018?
Formula: (C5 + B5)/2 
Formula2: (C5 + B5)/2 
Level: Calculation
Question: What is the average off-net revenue earned by the company in 2017 and 2018?
Formula: (C6 + B6)/2 
Formula2: (C6 + B6)/2 
Level: Calculation