Seems like Q2 has insufficient data or the data is hidden above the text 'an environmental study indicates that...'

What u mean

For part (a) we can simply differentiate the expression c with respect to p (i.e. c'(p) or dc/dp and then substitute p = 18 to the result.

For part (b), however, since the question asks 'at what rate...with respect to time', we need to find c'(t) or dc/dt, but there is no expression for c in terms of t. I tried to make sense of the word 'average daily level', but could not obtain much useful information from here.

Sorry I just saw the above part on the previous page

I had post out the qns at the answer there