If we divide by (x − r), we let x = r.
Hence, if we divide by (x + 4), we let x = -4.
Therefore the remainder
R = f(-4) = 3(-4)3 - (-4)2 - 20(-4) + 5 = -192 - 16 + 80 + 5 = -123
= 3(-4)3 - (-4)2 - 20(-4) + 5
= -192 - 16 + 80 + 5
= -123