how can i do calcualtion while hadling the datatype problem?

actually i am making a project of a book store software and as i am a student so i don't know how to handle the following situaation

ok i have to deal with three variables
i do it like this
dim x as decimal
dim y as decimal
dim z as decimal

if combo.selectedtext = "fantasy"
x=24
else x=0
end if

y=23
and z=x+y

now the problem comes with display

i mean i do it like in text boxes
so taxoutput.tostring.contains "23"
it comes but not x and y it shows them as x and y and x+y in case of z when i put it like in string contain thing. please help me.