Is negative 73 a natural number

The graph below shows the price of different numbers of mats at a store: a graph is shown. the values on the x axis are 0, 2, 4, 6, 8, 10. the values on the y axis are 0, 21, 42, 63, 84, and 105. points are shown on ordered pairs 0, 0 and 2, 21 and 4, 42 and 6, 63 and 8, 84. these points are connected by a line. the label on the x axis is number of mats. the title on the y axis is price in dollars. which equation can be used to determine p, the cost of b mats?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

Stephen thublin invests $1,000,000 in a 45-day certificate of deposit with 6.55% interest. what is the total interest income from the investment?