Please answer all the questions in the image, please.

4. A marketing agency has launched a new video. They estimate that the proportion p of their target audience that has seen the video at time t [measured in hours} is given by 1 t =. M 2' 1 + Hie-U2 (a) 1 point How long will it take for 90% of the target audience to see the video? (b) At what rate is the proportion of viewers changing when 50% of the target audience has seen the video