i would say "B"
blue chairs to red chairs is 2 to 5
so as a fractoon blue chairs are 2/7 and red chairs are 5/7.
since it is out of 7 i divide the total number of chairs by 7
a) 21/7= 3
3(2):3(5)
6:15 and this simplifies to 2:5
b)30/7 i would say would not work since it doesn't multiply into 30
c)28/7=4
4(2):4(5)
8:20 and this also simply to 2:5
d) 35/7=5
5(2):5(5)
10:25 this aswell simplifies to 2:5
so "B" is your answer since ut won't work