Find the force in member AC for the pin-jointed structure below. (by convention: positive indicates tension, negative indicates compression)

A. $-80$ $kN$
B. $-51$ $kN$
C. $-48$ $kN$
D. $-45$ $kN$
E. $-19$ $kN$
F. $19$ $kN$
G. $45$ $kN$
H. $48$ $kN$
I. $51$ $kN$
J. $80$ $kN$