Give the step-by-step reasoning process and then the final answer. 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 = 70 seashells. In two weeks there will be 70 + 20 = 90 seashells. In three weeks there will be 90 + 20 = 110 seashells. In four weeks there will be 110 + 20 = 130 seashells.
The final answer: 130.