Question 879033
What is the great common factor of 126 and 588?
Factors of 126 = 1, 2, 3, 6, 7, 9, 14, 18, 21, 42, 63, 126. 
Factors of 588 = 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 49, 84, 98, 147, 196, 294, 588. 
The great number they have in common is 42.  Assuming all rows to be equal (42 chairs per row), there will be:
{{{126/42}}} rows of chairs for the graduates [3 rows], and
{{{588/42}}} rows of chairs for the guests [14 rows]