It has a solution, but it isn't a positive number, it's a negative one (which you probably didn't get to jet at school, so teacher said it hasn't got a solution)
8X + 19 = 11
move every normal number without X to one side (remember, when moving number across sides, change its sign)
8X = 11 - 19
now
8X = -8
and you get X that is a negative
X = -8/8
X = -1