a) goes exactly in the middle between 4/10 and 5/10 on the numberline
b) exactly in the middle between 3/10 and 4/10
c) split the line in half between 7/10 and 8/10, then make a line at the center on the left side (basically split the line into 4 parts and mark it as the 1st line)
d/e/f) do the same as in C but between 2/10 and 3/10
