proof that i'm really very sick of marking

Assuming a teacher has 300 scripts to mark. Given that the teacher has 7 days to complete the entire stack (yes, sadly teachers work over the weekend too):

(a) Calculate how many scripts the teacher must mark per day to complete her marking [1] (b) Assuming the teacher has other duties to attend to for 3 hours per day (well, you know), and spends the rest of the day marking (with no sleep), calculate how many scripts she must mark per day to complete her marking in time. [2] (c) Given that the teacher’s speed of marking is x, calculate the diminishing marginal rate of return for this teacher. [4]