Nathan collected 6 bags of seashells . There were 20 seashells in the first bag . There were 20 more seashells in the second bag than first bag . There were 20 more seashells in the third bag than the second bag and so on . He then put all the seashells equally into 4 similar boxes .

a) How many seashells were there in 6 bags altogether ?

b) How many seashells were there in each box ?​