What is the smallest and most elementary type of family organization ?

H=height
y=number of years.

we have the next expresion:
h(y)=my+b  

m=the slope of the line, in this case, the slope is equal to "18"; (18 cm/ year).
b=the initial heigth, in this case, the initial heigth is equal to "5" (5 cm).

Therefore, our  expression will be:
h(y)=18y +5

h(y)=18y+5