The suns energy reaches the sun by
conduction
convection
radiation
fusion

Radiation

Explanation:

Radiation.

It is by Radiation.

Conduction of heat is the process by which heat energy is transferred through a material, the average position of the particles of the material remaining the same. eg cloth, cork, wood etc.

Convection is the process by which heat is transferred in a liquid or gas by the actual movement of the heated fluid from the hotter to the colder parts.

Radiation is the process by which heat is transferred from a hotter to a cooler place with heating of the intervening medium.

Fusion(melting) is the process whereby a substance changes from solid state to a liquid state when heat is applied to it.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.