How did he tell that the peak does not have a zero background? How do we know if we have zero background from a graph like this?

Question 3) Peak area for a symmetric peak can be calculated from the formula A = h x W1/2 8 7 6 5 4 W1/2 = 5 3 2 1 h = 7.2 0 190 -1 195 200 205 210 215 220 225 230 Calculate the area of this peak using the formula above. Is there anything notable about this peak? A = h x W1/2 = 7.2 x 5 = 36 This peak does not have a zero background, especially on the right hand side. This could be due to matrix effect, a broad additional peak to the right, unexpected retention, or some other analytical artefact