For this case, what we are going to do first is to assume that all the exams are worth the same percentage of the final grade.
We have then that Lisa's average grade point equation is:

Where,
x: minimum note that lisa must obtain in the last exam.
Clearing x we have:
Answer:
the lowest grade she can get on her last test is:
x = 94
15h^2 +10h +25 /5h = x +y +
15h^2 +10h +25/5h = 3h +2
15h^2
---------
0 10h
10h
------
0 25
so x=3h and y =2 than the 3rd choice is correct ,right sure
Joan's remaining distance is reduced by (600 ft)/(3 hours) = 200 ft/hour. She starts with 1600 ft remaining, so her distance remaining (y) after x hours is
.. y = -200x +1600
In order for the distance remaining to be zero, you must have
.. 0 = -200x +1600
.. 200x = 1600
.. x = 1600/200 = 8
It will take Joan 8 hours to hike 1600 ft.