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