You didn't describe the situation so I can't answer.
However: if the graph of the situation is a straight line then the situation is linear, and if the graph is not a straight line then it is nonlinear.
You did not provide us with equations to select.
Find the slope m.
m = (1 - 2)/(3 - (-1))
m = -1/(3 + 1)
m = -1/4
Use the slope and one of the points and plug into the point-slope formula.
y - 1 = (-1/4)(x - 3)
Isolate y.
y - 1 = (-1/4)x + (3/4)
y = (-1/4)x + (3/4) + 1
y = (-1/4)x + (7/4)
Did you follow?
