I added a screenshot of the question
Part (A):
Since the two figure are similar, therefore, we will use the similarity proportionality to get the unknown side as follows:
[tex] \frac{16}{8}  =  \frac{x}{2} [/tex]
x = [tex] \frac{2*16}{8}  = 4 units[/tex]
Part (B):
Since the two figures are similar, therefore, we will use similarity proportionality to get the unknown sides as follows:
[tex] \frac{y}{8}  =  \frac{12}{4}  =  \frac{18}{x} [/tex]
x = [tex] \frac{18*4}{12}  = 6 units[/tex]
y = [tex] \frac{12*8}{4}  = 24 units[/tex]
Hope this helps :)