For this we simply write it out as two expressions. Then set them equal to each other, because they have the same # of chairs available to them. (Zero being having no chair left over)
r = # of chairs in a given row (They are all the same according to the text)
9r + 3
7r + 19
9r + 3 = 7r + 19
Move 7r to the left side by subtracting it on both sides.
9r + 3 - 7r = 19
Simplify!
2r + 3 = 19
Subtract the 3 from both sides!
2r = 19 - 3
Simplify!
2r = 16
Divide by 2 on both sides to get r alone.
r = 16/2
Simplify.
r = 8
Now to make sure we got the correct value we should plug it into the equations we derived from the problem.
9(8) + 3 = 7(8) + 19
75 = 75
So that checks out!
(Also that is the number of chairs.. :p)
So our answer is!
# Of Chairs = 75
