Which of the following was not an african empire at one point?
a. ghana
b. mali
c. songhai
d. liberia

D. Liberia

Explanation:

Liberia is also described as one of two African nations which have remain independent during the European tussle for Africa, The country Liberia was founded by the African-Americans in the 1820s.      

Later the Americo-Liberian government was overthrown in 1989 and then it was governed by the military coup until 1990 and then this country is suffered from Civil wars.

In 2005 Ellen Johnson elected as the new president of Liberia.

(4,-2)

explanation:

6x+4y=16

-6x-9y=-6

-5y=10

y=-2

x=4