Answer:
R = rows
C = columns
The chairs will be arranged in a way such that R * C [tex]\geq[/tex] 70
We know that R [tex]\leq[/tex] 20
70 / 20 = 3.5; however, you can't have half of a chair.
So find all the factors of 70 which don't exceed 20.
1, 70
2, 35