tolong bantuan nya ya kak nomer 20 beserta caranya

f(x) = ax + b
f(1) = 11
f(4) = 20

[tex]f(x) = ax + b \\ a \times 1 + b = 11 \\ a + b = 11 \\ \\ a \times 4 + b = 20 \\ 4a + b = 20 \\ \\ a \: \: + b = 11 \\ 4a + b = 20[/tex]
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[tex] - 3a = - 9 \\ a = \frac{ - 9}{ - 3} \\ a = 3 \\ \\ a + b = 11 \\ 3 + b = 11 \\ b = 11 - 3 \\ b = 8 \\ \\ f( - 1) : \\ = ax + b \\ = 3 \times - 1 + 8 \\ = - 3 + 8 \\ = 5[/tex]

☛️ Jawabannya : B.