we have that
2y-8x=5x-12----> 2y=13x-12
we know that
If point C, (4, n) lies on this straight line
so
in the straight line
for x=4
the value of y must be n
2y=13x-12-----> 2y=13*4-12----> 2y=52-12----> 2y=40----> y=20
the value of n must be 20
the answer is
n is 20