The ratio that is not equivalent is B. 7:15
The reason why it's not equivalent because for the other ratios:
1:5 could be turned into 2:10 by multiplying 1 and 5 by 2.
4:20 could turn into 2:10 by dividing both numbers by 2.
And 8:40 could be divided by 4 to get 2:10.
But you can't do anything to 7:15 to make it 2:10.