Each week Carina puts 20 more seashells in a jar than she did the week before. If there are 50 seashells in the jar this week, how many will there be in a month?
In one week there will be 50+20=<T>add(50, 20)=70 seashells
In two weeks there will be 70+20=<T>add(70, 20)=90 seashells
In three weeks there will be 90+20=<T>add(90, 20)=110 seashells
In four weeks there will be 110+20=<T>add(110, 20)=130 seashells
