Question

the difference between two whole number is 26 and one number is three times the other then the smaller number is..........my work x-y=26,3x_y=26

Answer 1

looks like you defined the larger as x
and the smaller as y
so x - y = 26 is correct

then....
"one number is three times the other " ---> x = 3y

now sub that into the first equation:
x - y = 26
3y - y = 26
2y = 26
y = 13
then x = 3y = 3(13) = 39