The grades of six students are given by the equations below, where time is measured in weeks since the first midterm exam.

a) Alex's grade has been decreasing since the first exam. Which formula(s) could represent her grade?

b) Which student's grade is falling the fastest?

c) Umar's grade has been rising since the first exam; Which formula(s) could represent his grade?

d) Which student's grade is rising the fastest?

e) Karan came out of the first exam with a 85% in the class; which formula(s) could represent his grade?