How tall will i be at 18 if i am 5'9 at 15 my mum is 5'6 and my dad is 5'8?

chances are that you may be taller, but genetics are a lottery, and also you have external factors that develop the phenotype, eg. i smoked during my teens, I'm now 5' 7'' :(

phenotype is what effect the world has on the genotype, pretty much