Table:
0
A
B
C
D
1
Year Ended December 31
Percent Change
2
2019
2018
Change
3
(in thousands)
4
Service revenue
$546,159
$520,193
5.0%
5
On-net revenues
396,753
374,555
5.9%
6
Off-net revenues
148,931
145,004
2.7%
7
Network operations expenses(1)
219,801
219,526
0.1%
8
Selling, general, and administrative expenses(2)
146,913
133,858
9.8%
9
Depreciation and amortization expenses
80,247
81,233
(1.2)%
10
Gains on equipment transactions
1,059
982
7.8%
11
Interest expense
57,453
51,056
12.5%
12
Income tax expense
15,154
12,715
19.2%

Questions and formulas:
Question: What is the average service revenue in 2018 and 2019?
Formula: (C4 + B4)/2 
Formula2: (C4 + B4)/2 
Level: Calculation
Question: What is the average on-net revenue in 2018 and 2019?
Formula: (C5 + B5)/2 
Formula2: (C5 + B5)/2 
Level: Calculation
Question: What is the average off-net revenue in 2018 and 2019?
Formula: (C6 + B6)/2 
Formula2: (C6 + B6)/2 
Level: Calculation