Answer :
If f(1) = 1 that means c is -2 because when you substitute x = 1 and when c = -2, you'll get f(1) = -2(1)+3 = -2+3 = 1
So the constant c is -2 and that means the value of f(-4) is
f(-4)=-2(-4)+3=8+3=11
Thus, the value of f(-4) is 11.
About why does "c" have to be -2, here's the proof.
Given y = f(x), therefore.
y=cx+3
Since when x = 1 and y = 1, then Substitute x = 1 and y = 1, thus 1 = c+3
1 - 3 = c and therefore, -2 = c #
So this is the proof that c = -2