Find the annual rate of interest.
Principal = 7800
Period = 7
Total amount = 11349

I'm assuming your problem is about an arithmetic sequence, with first term equal to -10 and a common difference of 3 (meaning add 3 to a term to get the next term.

The first six terms are -10, -7, -4, -1, 2, 5.

To make a graph, plot points (1, -10), (2, -7), (3, -4), (4, -1), (5, 2), and (6, 5). See the attached picture. The points go steadily uphill, in a straight line. Any arithmetic sequence with a positive common difference will do just that!

Hope this helps!