5. In order to graduate, you must take at least 13 core credits and 6 electives credits and you can take no more than a total of 27 credits. Write a system of inequalities that defines how many of each you can take.
a C ≥ 13, E ≥ 6, C + E ≤ 27
b C+ E ≥ 19, C + E ≤ 27
c C ≤ 13, E ≤ 6, C + E ≤ 27
d C + E ≥ 19, C + E < 27