-13
step-by-step explanation:
f(x)=2x-5 for f(-4)
f(-4) means let x=-4
f(-4) = 2(-4) -5
f(-4) =-8-5
= -13
3, 12, 48, 384, 1536, 6144, 24576, 98304
just keep timing it by 4.