Let the row length = L
This implies that, since the number of total chairs is the same in each case, we have
5L + 3 = 3L + 21 subtract 3L, 3 from both sides
2L = 18 divide both sides by 2
L = 9 [ 9 chairs in a row ]
So......the total number of chairs = 5(9) + 3 = 48
Explanation