In the equation y=-3x as x increases what does y do

Because the slope is negative, you would expect that y decreases and x increases. To check this, you can substitute values for x. At x=0, y=0. Increase x to 1, and y=-3.

If x increases then y will decrease

prove:

y = - 3x

if x = - 1, then y = - 3 (-1) = 3

if x = 0, then y = - 3 (0) = 0

if x = 1, then y = - 3 (1) = - 3

if x = 2, then y = - 3 (2) = - 6

if x = 3, then y = - 3 (3) = - 9

and so on ...