Explanation:
It will be the equation of a line with negative slope
y = mx + b m = slope b = y-axis intercept
Pick two convenient points ( -20,0) and (30,-90 )
Slope = (y1-y2) / x1-x2) = (0 - - 90) / (-20 - 30) = 90/-50 = - 9/5
so far y = -9/5 x + b Plug in any point ( -70, 90) to calculate 'b'
90 = -9/5 (-70) + b shows b = -36
f(x) = -9/5x -36