How much heat is required to convert 2.55g of water at 28 degrees c to steam?

There are two different processes here:
1) we must add heat in order to bring the temperature of the water from  to  (the temperature at which the water evaporates)
2) other heat must be added to make the water evaporates

1) The heat needed for process 1) is

where 
is the water mass
is the water specific heat
is the variation of temperature of the water
If we plug the numbers into the equation, we find


2) The heat needed for process 2) is

where 
is the water mass
is the latent heat of evaporation of water
If we plug the numbers into the equation, we find


So, the total heat needed for the whole process is

Divide 108.2 x 10^6 into 1.5 x 10 and the result will be in au (astronomical units)