Trên bóng đèn có ghi là 12v -6w. Khi đèn sáng bình thường thì dòng điện chạy qua đèn có cường độ là

the current is 0.6

voltage ÷ resistance = current

so 12 ÷ 20 = 0.6

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m