The graph below shows the volume of carbon dioxide captured, VVV (in cubic metres, m3\text{m}^3m3), by an experimental carbon capture unit over a period of t t\,t minutes.

Draw a tangent to the curve at t=80 minutest = 80\text{ minutes}t=80 minutes.
Use this tangent to calculate the rate of carbon dioxide capture at t=80 minutest = 80\text{ minutes}t=80 minutes.