Diketahui f(4x-1)=8x+4 nilai f(3) adalah..

f(4x-1) = 8x+4
f(4x-1) = 2 (4x-1) = 8×-2
= 2x+6
f(3)=2×3+6
=12

4x - 1 = a
4x = a+1
x = a+1 / 4

maka 
f(a) = 8(a+1 / 4) + 4
f(a) = 2(a+1) + 4
f(a) = 2a + 2 + 4
f(a) = 2a + 6

jadi
f(3) = 2(3) + 6
f(3) = 6 + 6
f(3) = 12