Write an equation for the nth term of the arithmetic sequence of -3,-1,1,3

On a piece of paper, graph . then determine which answer choice matches the graph you drew

The magnitude, m, of an earthquake is defined to be m=log l/s, where i is the intensity of the earthquake (measured by the amplitude of the seismograph wave) and s is the intensity of a “standard” earthquake, which is barely detectable. what is the magnitude of an earthquake that is 1,000 times more intense than a standard earthquake? use a calculator. round your answer to the nearest tenth.

How do you use the elimination method for this question? explain, because i really want to understand!