9x + 3 = 7x +19
2x + 3 = 19
2x = 16
x = 8
So, x (8) is the number of chairs in each row with these setups.
Plug 8 into one of the equations and you will find how many chairs total there are.
9(8) + 3 = 75
There are 75 chairs total
The common difference is 12
Further explanation:
It is given that the infinite sequence is an arithmetic sequence
The common difference is the difference between consecutive terms of an arithmetic sequence.
Here,

The common difference is denoted by d.
Here,

The common difference is same for all proceeding terms.
So,
d = 12
Keywords: Infinite arithmetic sequence, Common difference
Learn more about arithmetic sequence at:
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A. Multiplication is the ONLY function that reverses what division did. If you did 56/-14 = n, then n x -14 should equal 56.
-2.8 • -2.8 • -2.8 • -2.8 • -2.8 • -2.8
=481.890