tolong dijawab, ditumpuk besok

f(x) = 4 - 2x
f(b) = 10
..........................

f(x) = 4 - 2x
f(10) = 4 - 2b
10 - 4 = 2b
8 = 2b
4 = b
..........................

maaf kalau ada kesalahan semoga membantu yaa...