`b)`
`4^x + 4^{x+3} = 4160`
`=> 4^x + 4^x . 4^3 = 4160`
`=> 4^x (1+ 4^3) = 4160`
`=> 4^x . 65 = 4160`
`=> 4^x = 64`
`=> 4^x = 4^3`
`=> x = 3`
Vậy `x=3`
`c)`
`4^{x+3} - 3 . 4^{x+1} = 13 . 4^11`
`=> 4^{x+1} . 4^2 - 3 . 4^{x+1} = 13 . 4^11`
`=> 4^{x+1} . (4^2 - 3) = 13 . 4^11`
`=> 4^{x+1} . 13 = 13 . 4^11`
`=> 4^{x+1} = 4^11`
`=> x+1=11`
`=>x=10`
Vậy `x=10`
`d)`
`3 . 2^{x} + 5 . 2^{x} = 64 . 2^12`
`=> 2^{x} . (3 + 5) = 2^6 . 2^12`
`=> 2^{x} . 8 = 2^18`
`=> 2^{x} . 2^3 = 2^18`
`=> 2^{x+3} = 2^18`
`=>x+3=18`
`=>x=15`
Vậy `x=15`
