Let x be the number of weeks and y be the amount of waste. The linear equation may be expressed as,
y = mx + b
where m and b are the slope and y - intercept, respectively. Substituting the corresponding values,
(Week 5) 40 = 5m + b
(Week 10) 30 = 10m + b
Solving for m and b gives the values as m = -2 and b =50. Thus, the equation is
y = -2x + 50
The answer is letter C.