gimana yah saya kurang mengerti ?

22. f(a) =8
f(x) = (x-3) / (x+4)
8 = (a- 3) / (a + 4 )
8 ( a + 4 ) = a - 3
8a + 32 = a - 3
8a - a = - 3 - 32
7a = - 35
a = - 35/7
a = - 5